FCC 79.101 as of October 1, 2020

Goto Section: 79.100 | 79.102 | Table of Contents

FCC 79.101
Revised as of October 1, 2020
Goto Year:2019 | 2021

§ 79.101 Closed caption decoder requirements for analog television
receivers.

(a)(1) Effective July 1, 1993, all television broadcast receivers with
picture screens 33 cm (13 in) or larger in diameter shipped in
interstate commerce, manufactured, assembled, or imported from any
foreign country into the United States shall comply with the provisions
of this section.

Note to paragraph (a)(1): This paragraph places no restriction on the
shipping or sale of television receivers that were manufactured before
July 1, 1993.

(2) Effective January 1, 2014, all television broadcast receivers
shipped in interstate commerce, manufactured, assembled, or imported
from any foreign country into the United States shall comply with the
provisions of this section, if technically feasible, except that
television broadcast receivers that use a picture screen less than 13
inches in size must comply with the provisions of this section only if
doing so is achievable pursuant to § 79.103(b)(3).

Note to paragraph (a)(2): This paragraph places no restrictions on the
importing, shipping, or sale of television receivers that were
manufactured before January 1, 2014.

(b) Transmission format. Closed-caption information is transmitted on
line 21 of field 1 of the vertical blanking interval of television
signals, in accordance with § 73.682(a)(22) of this chapter.

(c) Operating modes. The television receiver will employ
customer-selectable modes of operation for TV and Caption. A third mode
of operation, Text, may be included on an optional basis. The Caption
and Text Modes may contain data in either of two operating channels,
referred to in this document as C1 and C2. The television receiver must
decode both C1 and C2 captioning, and must display the captioning for
whichever channel the user selects. The TV Mode of operation allows the
video to be viewed in its original form. The Caption and Text Modes
define one or more areas (called "boxes") on the screen within which
caption or text characters are displayed.

Note: For more information regarding Text mode, see "Television
Captioning for the Deaf: Signal and Display Specifications",
Engineering Report No. E-7709-C, Public Broadcasting Service, dated May
1980, and "TeleCaption II Decoder Module Performance Specification",
National Captioning Institute, Inc., dated November 1985. These
documents are available, respectively, from the Public Broadcasting
Service, 1320 Braddock Place, Alexandria, VA 22314 and from the
National Captioning Institute, Inc., 5203 Leesburg Pike, Falls Church,
VA 22041.

(d) Screen format. The display area for captioning and text shall fall
approximately within the safe caption area as defined in paragraph
(n)(12) of this section. This display area will be further divided into
15 character rows of equal height and 32 columns of equal width, to
provide accurate placement of text on the screen. Vertically, the
display area begins on line 43 and is 195 lines high, ending on line
237 on an interlaced display. All captioning and text shall fall within
these established columns and rows. The characters must be displayed
clearly separated from the video over which they are placed. In
addition, the user must have the capability to select a black
background over which the captioned letters are displaced.

(1) Caption mode. In the Caption Mode, text can appear on up to 4 rows
simultaneously anywhere on the screen within the defined display area.
In addition, a solid space equal to one column width may be placed
before the first character and after the last character of each row to
enhance legibility. The caption area will be transparent anywhere that
either:

(i) No standard space character or other character has been addressed
and no accompanying solid space is needed; or,

(ii) An accompanying solid space is used and a "transparent space"
special character has been addressed which does not immediately precede
or follow a displayed character.

(2) [Reserved]

(e) Presentation format. In analyzing the presentation of characters,
it is convenient to think in terms of a non-visible cursor which marks
the screen position at which the next event in a given mode and data
channel will occur. The receiver remembers the cursor position for each
mode even when data are received for a different address in an
alternate mode or data channel.

(1) Screen addressing. Two kinds of control codes are used to move the
cursor to specific screen locations. In Caption Mode, these addressing
codes will affect both row and column positioning. In Text Mode, the
codes affect only column positioning. In both modes, the addressing
codes are optional. Default positions are defined for each mode and
style when no addressing code is provided.

(i) The first type of addressing code is the Preamble Address Code
(PAC). It assigns a row number and one of eight "indent" figures. Each
successive indent moves the cursor four columns to the right (starting
from the left margin). Thus, an indent of 0 places the cursor at Column
1, an indent of 4 sets it at Column 5, etc. The PAC indent is
non-destructive to displayable characters. It will not affect the
display to the left of the new cursor position on the indicated row.
Note that Preamble Address Codes also set initial attributes for the
displayable characters which follow. See paragraph (h) of this section
and the Preamble Address Code table.

(ii) The second type of addressing code is the Tab Offset, which is one
of three Miscellaneous Control Codes. Tab Offset will move the cursor
one, two, or three columns to the right. The character cells skipped
over will be unaffected; displayable characters in these cells, if any,
will remain intact while empty cells will remain empty, in the same
manner that a PAC indent is non-destructive.

(2) [Reserved]

(f) Caption Mode. There are three styles of presenting text in Caption
Mode: roll-up, pop-on, and paint-on. Character display varies
significantly with the style used, but certain rules of character
erasure are common to all styles. A character can be erased by
addressing another character to the same screen location or by
backspacing over the character from a subsequent location on the same
row. The entire displayed memory will be erased instantly by receipt of
an Erase Displayed Memory command. Both displayed memory and
non-displayed memory will be entirely erased simultaneously by either:
The user switching receiver channels or data channels (C1/C2) or fields
(F1/F2) in decoders so equipped; the loss of valid data (see paragraph
(j) of this section); or selecting non-captioning receiver functions
which use the display memory of the decoder. Receipt of an End of
Caption command will cause a displayed caption to become non-displayed
(and vice versa) without being erased from memory. Changing the
receiver to a non-captioning mode which does not require use of the
decoder's display memory will leave that memory intact, and the decoder
will continue to process data as if the caption display were selected.

(1) Roll-up. Roll-up style captioning is initiated by receipt of one of
three Miscellaneous Control Codes that determine the maximum number of
rows displayed simultaneously, either 2, 3 or 4 contiguous rows. These
are the three Roll-Up Caption commands.

(i) The bottom row of the display is known as the "base row". The
cursor always remains on the base row. Rows of text roll upwards into
the contiguous rows immediately above the base row to create a "window"
2 to 4 rows high.

(ii) The Roll-Up command, in normal practice, will be followed (not
necessarily immediately) by a Preamble Address Code indicating the base
row and the horizontal indent position. If no Preamble Address Code is
received, the base row will default to Row 15 or, if a roll-up caption
is currently displayed, to the same base row last received, and the
cursor will be placed at Column 1. If the Preamble Address Code
received contains a different base row than that of a currently
displayed caption, the entire window will move intact (and without
erasing) to the new base row immediately.

(iii) Each time a Carriage Return is received, the text in the top row
of the window is erased from memory and from the display or scrolled
off the top of the window. The remaining rows of text are each rolled
up into the next highest row in the window, leaving the base row blank
and ready to accept new text. This roll-up must appear smooth to the
user, and must take no more than 0.433 second to complete. The cursor
is automatically placed at Column 1 (pending receipt of a Preamble
Address Code).

(iv) Increasing or decreasing the number of roll-up rows instantly
changes the size of the active display window, appropriately turning on
or off the display of the top one or two rows. A row which is turned
off should also be erased from memory.

(v) Characters are always displayed immediately when received by the
receiver. Once the cursor reaches the 32nd column position on any row,
all subsequent characters received prior to a Carriage Return, Preamble
Address Code, or Backspace will be displayed in that column replacing
any previous character occupying that address.

(vi) The cursor moves automatically one column to the right after each
character or Mid-Row Code received. A Backspace will move the cursor
one column to the left, erasing the character or Mid-Row Code occupying
that location. (A Backspace received when the cursor is in Column 1
will be ignored.)

(vii) The Delete to End of Row command will erase from memory any
characters or control codes starting at the current cursor location and
in all columns to its right on the same row. If no displayable
characters remain on the row after the Delete to End of Row is acted
upon, the solid space (if any) for that row should also be erased to
conform with the following provisions.

(viii) If a solid space is used for legibility, it should appear when
the first displayable character (not a transparent space) or Mid-Row
Code is received on a row, not when the Preamble Address Code, if any,
is given. A row on which there are no displayable characters or Mid-Row
Codes will not display a solid space, even when rolled up between two
rows which do display a solid space.

(ix) If the reception of data for a row is interrupted by data for the
alternate data channel or for Text Mode, the display of caption text
will resume from the same cursor position if a Roll-Up Caption command
is received and no Preamble Address Code is given which would move the
cursor.

(x) A roll-up caption remains displayed until one of the standard
caption erasure techniques is applied. Receipt of a Resume Caption
Loading command (for pop-on style) or a Resume Direct Captioning
command (for paint-on style) will not affect a roll-up display. Receipt
of a Roll-Up Caption command will cause any pop-on or paint-on caption
to be erased from displayed memory and non-displayed memory.

(2) Pop-on. Pop-on style captioning is initiated by receipt of a Resume
Caption Loading command. Subsequent data are loaded into a
non-displayed memory and held there until an End of Caption command is
received, at which point the non-displayed memory becomes the displayed
memory and vice versa. (This process is often referred to as "flipping
memories" and does not automatically erase memory.) An End of Caption
command forces the receiver into pop-on style if no Resume Caption
Loading command has been received which would do so. The display will
be capable of 4 full rows, not necessarily contiguous, simultaneous
anywhere on the screen.

(i) Preamble Address Codes can be used to move the cursor around the
screen in random order to place captions on Rows 1 to 15. Carriage
Returns have no effect on cursor location during caption loading.

(ii) The cursor moves automatically one column to the right after each
character or Mid-Row Code received. Receipt of a Backspace will move
the cursor one column to the left, erasing the character or Mid-Row
Code occupying that location. (A Backspace received when the cursor is
in Column 1 will be ignored.) Once the cursor reaches the 32nd column
position on any row, all subsequent characters received prior to a
Backspace, an End of Caption, or a Preamble Address Code, will replace
any previous character at that location.

(iii) The Delete to End of Row command will erase from memory any
characters or control codes starting at the current cursor location and
in all columns to its right on the same row. If no displayable
characters remain on a row after the Delete to End of Row is acted
upon, the solid space (if any) for that element should also be erased.

(iv) If data reception is interrupted during caption loading by data
for the alternate caption channel or for Text Mode, caption loading
will resume at the same cursor position if a Resume Caption Loading
command is received and no Preamble Address Code is given that would
move the cursor.

(v) Characters remain in non-displayed memory until an End of Caption
command flips memories. The caption will be erased without being
displayed upon receipt of an Erase Non-Displayed Memory command, a
Roll-Up Caption command, or if the user switches receiver channels,
data channels or fields, or upon the loss of valid data (see paragraph
(j) of this section).

(vi) A pop-on caption, once displayed, remains displayed until one of
the standard caption erasure techniques is applied or until a Roll-Up
Caption command is received. Characters within a displayed pop-on
caption will be replaced by receipt of the Resume Direct Captioning
command and paint-on style techniques (see below).

(3) Paint-on. Paint-on style captioning is initiated by receipt of a
Resume Direct Captioning command. Subsequent data are addressed
immediately to displayed memory without need for an End of Caption
command.

(i) Preamble Address Codes can be used to move the cursor around the
screen in random order to display captions on Rows 1 to 15. Carriage
Returns have no affect on cursor location during direct captioning. The
cursor moves automatically one column to the right after each character
or Mid-Row Code is received. Receipt of a Backspace will move the
cursor one column to the left, erasing the character or Mid-Row Code
occupying that location. (A Backspace received when the cursor is in
Column 1 will be ignored.) Once the cursor reaches the 32nd column
position on any row, all subsequent characters received prior to a
Preamble Address Code or Backspace will be displayed in that column
replacing any previous character occupying that location.

(ii) The Delete to End of Row command will erase from memory any
characters or control codes starting at the current cursor location and
in all columns to its right on the same row. If no displayable
characters remain on the row after the Delete to End of Row is acted
upon, the solid space (if any) for that element should also be erased.

(iii) If the reception of data is interrupted during the direct
captioning by data for the alternate caption channel or for Text Mode,
the display of caption text will resume at the same cursor position if
a Resume Direct Captioning command is received and no Preamble Address
Code is given which would move the cursor.

(iv) Characters remain displayed until one of the standard caption
erasure techniques is applied or until a Roll-Up Caption command is
received. An End of Caption command leaves a paint-on caption fully
intact in non-displayed memory. In other words, a paint-on style
caption behaves precisely like a pop-on style caption which has been
displayed.

(g) Character format. Characters are to be displayed on the screen
within a character "cell" which is the height and width of a single row
and column. The following codes define the displayable character set.
Television receivers manufactured prior to January 1, 1996 and having a
character resolution of 5 × 7 dots, or less, may display the allowable
alternate characters in the character table. A statement must be in a
prominent location on the box or other package in which the receiver is
to be marketed, and information must be in the owner's manual,
indicating the receiver displays closed captioning in upper case only.

Character Set Table

Special Characters

These require two bytes for each symbol. Each hex code as shown will be
preceded by a 11h for data channel 1 or by a 19h for data channel 2.
For example: 19h 37h will place a musical note in data channel 2.
HEX Example Alternate Description
30 � See note^1 Registered mark symbol
31 ° Degree sign
32 1/2 1/2
33 � Inverse query
34 ^TM See note^1 Trademark symbol
35 � Cents sign
36 � Pounds Sterling sign
37 d` Music note
38 � A Lower-case a with grave accent
39 Transparent space
3A � E Lower-case e with grave accent
3B � A Lower-case a with circumflex
3C � E Lower-case e with circumflex
3D � I Lower-case i with circumflex
3E � O Lower-case o with circumflex
3F � U Lower-case u with circumflex

^1Note: The registered and trademark symbols are used to satisfy
certain legal requirements. There are various legal ways in which these
symbols may be drawn or displayed. For example, the trademark symbol
may be drawn with the "T" next to the "M" or over the "M". It is
preferred that the trademark symbol be superscripted, i.e., XYZ^TM. It
is left to each individual manufacturer to interpret these symbols in
any way that meets the legal needs of the user.

Standard characters

HEX Example Alternate Description
20 Standard space
21 ! Exclamation mark
22 " Quotation mark
23 # Pounds (number) sign
24 $ Dollar sign
25 % Percentage sign
26 & Ampersand
27 ' Apostrophe
28 ( Open parentheses
29 ) Close parentheses
2A � A Lower-case a with acute accent
2B + Plus sign
2C , Comma
2D - Minus (hyphen) sign
2E . Period
2F / Slash
30 0 Zero
31 1 One
32 2 Two
33 3 Three
34 4 Four
35 5 Five
36 6 Six
37 7 Seven
38 8 Eight
39 9 Nine
3A : Colon
3B ; Semi-colon
3C < Less than sign
3D = Equal sign
3E > Greater than sign
3F ? Question mark
40 @ At sign
41 A Upper-case A
42 B Upper-case B
43 C Upper-case C
44 D Upper-case D
45 E Upper-case E
46 F Upper-case F
47 G Upper-case G
48 H Upper-case H
49 I Upper-case I
4A J Upper-case J
4B K Upper-case K
4C L Upper-case L
4D M Upper-case M
4E N Upper-case N
4F O Upper-case O
50 P Upper-case P
51 Q Upper-case Q
52 R Upper-case R
53 S Upper-case S
54 T Upper-case T
55 U Upper-case U
56 V Upper-case V
57 W Upper-case W
58 X Upper-case X
59 Y Upper-case Y
5A Z Upper-case Z
5B [ Open bracket
5C � E Lower-case e with acute accent
5D ] Close bracket
5E � I Lower-case i with acute accent
5F � O Lower-case o with acute accent
60 � U Lower-case u with acute accent
61 a A Lower-case a
62 b B Lower-case b
63 c C Lower-case c
64 d D Lower-case d
65 e E Lower-case e
66 f F Lower-case f
67 g G Lower-case g
68 h H Lower-case h
69 i I Lower-case i
6A j J Lower-case j
6B k K Lower-case k
6C l L Lower-case l
6D m M Lower-case m
6E n N Lower-case n
6F o O Lower-case o
70 p P Lower-case p
71 q Q Lower-case q
72 r R Lower-case r
73 s S Lower-case s
74 t T Lower-case t
75 u U Lower-case u
76 v V Lower-case v
77 w W Lower-case w
78 x X Lower-case x
79 y Y Lower-case y
7A z Z Lower-case z
7B � C Lower-case c with cedilla
7C � Division sign
7D � Upper-case N with tilde
7E � � Lower-case n with tilde
7F fS Solid block

(h) Character Attributes--(1) Transmission of Attributes. A character
may be transmitted with any or all of four attributes: Color, italics,
underline, and flash. All of these attributes are set by control codes
included in the received data. An attribute will remain in effect until
changed by another control code or until the end of the row is reached.
Each row begins with a control code which sets the color and underline
attributes. (White non-underlined is the default display attribute if
no Preamble Address Code is received before the first character on an
empty row.) Attributes are not affected by transparent spaces within a
row.

(i) All Mid-Row Codes and the Flash On command are spacing attributes
which appear in the display just as if a standard space (20h) had been
received. Preamble Address Codes are non-spacing and will not alter any
attributes when used to position the cursor in the midst of a row of
characters.

(ii) The color attribute has the highest priority and can only be
changed by the Mid-Row Code of another color. Italics has the next
highest priority. If characters with both color and italics are
desired, the italics Mid-Row Code must follow the color assignment. Any
color Mid-Row Code will turn off italics. If the least significant bit
of a Preamble Address Code or of a color or italics Mid-Row Code is a 1
(high), underlining is turned on. If that bit is a 0 (low), underlining
is off.

(iii) The flash attribute is transmitted as a Miscellaneous Control
Code. The Flash On command will not alter the status of the color,
italics, or underline attributes. However, any color or italics Mid-Row
Code will turn off flash.

(iv) Thus, for example, if a red, italicized, underlined, flashing
character is desired, the attributes must be received in the following
order: a red Mid-Row or Preamble Address Code, an italics Mid-Row Code
with underline bit, and the Flash On command. The character will then
be preceded by three spaces (two if red was assigned via a Preamble
Address Code).

(2) Display of attributes. The underline attribute will be displayed by
drawing a line beneath the character in the same color as the
character. The flash attribute will be displayed by causing the
character to blink from the display at least once per second. The
italic attribute must be capable of being displayed by either a special
italic font, or by the modification of the standard font by slanting.
The user may be given the option to select other methods of italic
display as well. The support of the color attributes is optional. If
the color attributes are supported, they will be displayed in the color
they have been assigned. If color attributes are not supported, the
display may be in color, but all color changes will be ignored.

(i) Control codes. There are three different types of control codes
used to identify the format, location, attributes, and display of
characters: Preamble Address Codes, Mid-Row Codes, and Miscellaneous
Control Codes.

(1) Each control code consists of a pair of bytes which are always
transmitted together in a single field of line 21 and which are
normally transmitted twice in succession to help insure correct
reception of the control instructions. The first of the control code
bytes is a non-printing character in the range 10h to 1Fh. The second
byte is always a printing character in the range 20h to 7Fh. Any such
control code pair received which has not been assigned a function is
ignored. If the non-printing character in the pair is in the range 00h
to 0Fh, that character alone will be ignored and the second character
will be treated normally.

(2) If the second byte of a control code pair does not contain odd
parity (see paragraph (j) of this section), then the pair is ignored.
The redundant transmission of the pair will be the instruction upon
which the receiver acts.

(3) If the first byte of the first transmission of a control code pair
fails the parity check, then that byte is inserted into the currently
active memory as a solid block character (7Fh) followed by whatever the
second byte is. Again, the redundant transmission of the pair will be
the controlling instruction.

(4) If the first transmission of a control code pair passes parity, it
is acted upon within one video frame. If the next frame contains a
perfect repeat of the same pair, the redundant code is ignored. If,
however, the next frame contains a different but also valid control
code pair, this pair, too, will be acted upon (and the receiver will
expect a repeat of this second pair in the next frame). If the first
byte of the expected redundant control code pair fails the parity check
and the second byte is identical to the second byte in the immediately
preceding pair, then the expected redundant code is ignored. If there
are printing characters in place of the redundant code, they will be
processed normally.

(5) There is provision for decoding a second data channel. The second
data channel is encoded with the same control codes and procedures
already described. The first byte of every control code pair indicates
the data channel (C1/C2) to which the command applies. Control codes
which do not match the data channel selected by the user, and all
subsequent data related to that control code, are ignored by the
receiver.

Mid-Row Codes
Data channel 1 Data channel 2 Attribute description
11 20 19 20 White.
11 21 19 21 White Underline.
11 22 19 22 Green.
11 23 19 23 Green Underline.
11 24 19 24 Blue.
11 25 19 25 Blue Underline.
11 26 19 26 Cyan.
11 27 19 27 Cyan Underline.
11 28 19 28 Red.
11 29 19 29 Red Underline.
11 2A 19 2A Yellow.
11 2B 19 2B Yellow Underline.
11 2C 19 2C Magenta.
11 2D 19 2D Magenta Underline.
11 2E 19 2E Italics.
11 2F 19 2F Italics Underline.

Miscellaneous Control Codes
Data channel 1 Data channel 2 Mne-
monic Command description
14 20 1C 20 RCL Resume caption loading.
14 21 1C 21 BS Backspace.
14 22 1C 22 AOF Reserved (formerly Alarm Off).
14 23 1C 23 AON Reserved (formerly Alarm On).
14 24 1C 24 DER Delete to End of Row.
14 25 1C 25 RU2 Roll-Up Captions-2 Rows.
14 26 1C 26 RU3 Roll-Up Captions-3 Rows.
14 27 1C 27 RU4 Roll-Up Captions-4 Rows.
14 28 1C 28 FON Flash On.
14 29 1C 29 RDC Resume Direct Captioning.
14 2A 1C 2A TR Text Restart.
14 2B 1C 2B RTD Resume Text Display.
14 2C 1C 2C EDM Erase Displayed Memory.
14 2D 1C 2D CR Carriage Return.
14 2E 1C 2E ENM Erase Non-Displayed Memory.
14 2F 1C 2F EOC End of Caption (Flip Memories).
17 21 1F 21 TO1 Tab Offset 1 Column.
17 22 1F 22 TO2 Tab Offset 2 Columns.
17 23 1F 23 TO3 Tab Offset 3 Columns.

Preamble Address Codes
Row 1 Row 2 Row 3 Row 4 Row 5 Row 6 Row 7 Row 8 Row 9 Row 10 Row 11
Row 12 Row 13 Row 14 Row 15
First byte of code pair:
Data Channel 1 11 11 12 12 15 15 16 16 17 17 10 13 13 14 14
Data Channel 2 19 19 1A 1A 1D 1D 1E 1E 1F 1F 18 1B 1B 1C 1C
Second byte of code pair:
White 40 60 40 60 40 60 40 60 40 60 40 40 60 40 60
White Underline 41 61 41 61 41 61 41 61 41 61 41 41 61 41 61
Green 42 62 42 62 42 62 42 62 42 62 42 42 62 42 62
Green Underline 43 63 43 63 43 63 43 63 43 63 43 43 63 43 63
Blue 44 64 44 64 44 64 44 64 44 64 44 44 64 44 64
Blue Underline 45 65 45 65 45 65 45 65 45 65 45 45 65 45 65
Cyan 46 66 46 66 46 66 46 66 46 66 46 46 66 46 66
Cyan Underline 47 67 47 67 47 67 47 67 47 67 47 47 67 47 67
Red 48 68 48 68 48 68 48 68 48 68 48 48 68 48 68
Red Underline 49 69 49 69 49 69 49 69 49 69 49 49 69 49 69
Yellow 4A 6A 4A 6A 4A 6A 4A 6A 4A 6A 4A 4A 6A 4A 6A
Yellow Underline 4B 6B 4B 6B 4B 6B 4B 6B 4B 6B 4B 4B 68 4B 6B
Magenta 4C 6C 4C 6C 4C 6C 4C 6C 4C 6C 4C 4C 6C 4C 6C
Magenta Underline 4D 6D 4D 6D 4D 6D 4D 6D 4D 6D 4D 4D 6D 4D 6D
White Italics 4E 6E 4E 6E 4E 6E 4E 6E 4E 6E 4E 4E 6E 4E 6E
White Italics Underline 4F 6F 4F 6F 4F 6F 4F 6F 4F 6F 4F 4F 6F 4F 6F
Indent 0 50 70 50 70 50 70 50 70 50 70 50 50 70 50 70
Indent 0 Underline 51 71 51 71 51 71 51 71 51 71 51 51 71 51 71
Indent 4 52 72 52 72 52 72 52 72 52 72 52 52 72 52 72
Indent 4 Underline 53 73 53 73 53 73 53 73 53 73 53 53 73 53 73
Indent 8 54 74 54 74 54 74 54 74 54 74 54 54 74 54 74
Indent 8 Underline 55 75 55 75 55 75 55 75 55 75 55 55 75 55 75
Indent 12 56 76 56 76 56 76 56 76 56 76 56 56 76 56 76
Indent 12 Underline 57 77 57 77 57 77 57 77 57 77 57 57 77 57 77
Indent 16 58 78 58 78 58 78 58 78 58 78 58 58 78 58 78
Indent 16 Underline 59 79 59 79 59 79 59 79 59 79 59 59 79 59 79
Indent 20 5A 7A 5A 7A 5A 7A 5A 7A 5A 7A 5A 5A 7A 5A 7A
Indent 20 Underline 5B 7B 5B 7B 5B 7B 5B 7B 5B 7B 5B 5B 7B 5B 7B
Indent 24 5C 7C 5C 7C 5C 7C 5C 7C 5C 7C 5C 5C 7C 5C 7C
Indent 24 Underline 5D 7D 5D 7D 5D 7D 5D 7D 5D 7D 5D 5D 7D 5D 7D
Indent 28 5E 7E 5E 7E 5E 7E 5E 7E 5E 7E 5E 5E 7E 5E 7E
Indent 28 Underline 5F 7F 5F 7F 5F 7F 5F 7F 5F 7F 5F 5F 7F 5F 7F

Note: All indent codes (second byte equals 50h-5fh, 70th-7fh) assign
white as the color attribute.

(j) Data rejection. The receiver should provide an effective procedure
to verify data. A receiver will reject data if the data is invalid, or
if the data is directed to the data channel or field not selected by
the user. Invalid data is any data that fails to pass a check for odd
parity, or which, having passed the parity check, is assigned no
function.

(1) If a print character fails to pass a check for parity, a solid
block (7Fh) should be displayed in place of the failed character. In
addition, valid data can be corrupted in many ways and may not be
suitable for display. For example, repeated fields, skipped fields and
altered field sequences are all possible from consumer video equipment
and might present meaningless captions.

(2) The receiver will ignore data rejected due to being directed to a
deselected field or channel. However, this will not cause the display
to be disabled.

(k) Automatic display enable/disable. The receiver shall provide an
automatic enable/disable capability to prevent the display of invalid
or incomplete data, when the user selects the Caption Mode. The display
should automatically become enable after the receiver verifies the data
as described in paragraph (j) of this section. The display will be
automatically disabled when there is a sustained detection of invalid
data. The display will be re-enabled when the data verification process
has been satisfied once again.

(l) Compatibility with Cable Security Systems. Certain cable television
security techniques, such as signal encryption and copy protection, can
alter the television signal so that some methods of finding line 21
will not work. In particular, counting of lines or timing from the
start of the vertical blanking interval may cause problems. Caption
decoding circuitry must function properly when receiving signals from
cable security systems that were designed and marketed prior to April
5, 1991. Further information concerning such systems is available from
the National Cable Television Association, Inc., Washington, DC, and
from the Electronic Industries Association, Washington, DC.

(m) [Reserved]

(n) Glossary of terms. The following terms are used to describe caption
decoder specifications:

(1) Base row: The bottom row of a roll-up display. The cursor always
remains on the base row. Rows of text roll upwards into the contiguous
rows immediately above the base row.

(2) Box: The area surrounding the active character display. In Text
Mode, the box is the entire screen area defined for display, whether or
not displayable characters appear. In Caption Mode, the box is
dynamically redefined by each caption and each element of displayable
characters within a caption. The box (or boxes, in the case of a
multiple-element caption) includes all the cells of the displayed
characters, the non-transparent spaces between them, and one cell at
the beginning and end of each row within a caption element in those
decoders that use a solid space to improve legibility.

(3) Caption window: The invisible rectangle which defines the top and
bottom limits of a roll-up caption. The window can be 2 to 4 rows high.
The lowest row of the window is called the base row.

(4) Cell: The discrete screen area in which each displayable character
or space may appear. A cell is one row high and one column wide.

(5) Column: One of 32 vertical divisions of the screen, each of equal
width, extending approximately across the full width of the safe
caption area as defined in paragraph (n)(12) of this section. Two
additional columns, one at the left of the screen and one at the right,
may be defined for the appearance of a box in those decoders which use
a solid space to improve legibility, but no displayable characters may
appear in those additional columns. For reference, columns may be
numbered 0 to 33, with columns 1 to 32 reserved for displayable
characters.

(6) Displayable character: Any letter, number or symbol which is
defined for on-screen display, plus the 20h space.

(7) Display disable: To turn off the display of captions or text (and
accompanying background) at the receiver, rather than through codes
transmitted on line 21 which unconditionally erase the display. The
receiver may disable the display because the user selects an alternate
mode, e.g., TV Mode, or because no valid line 21 data is present.

(8) Display enable: To allow the display of captions or text when they
are transmitted on line 21 and received as valid data. For display to
be enabled, the user must have selected Caption Mode or Text Mode, and
valid data for the selected mode must be present on line 21.

(9) Element: In a pop-on or paint-on style caption, each contiguous
area of cells containing displayable characters and non-transparent
spaces between those characters. A single caption may have multiple
elements. An element is not necessarily a perfect rectangle, but may
include rows of differing widths.

(10) Erase Display: In Caption Mode, to clear the screen of all
characters (and accompanying background) in response to codes
transmitted on line 21. (The caption service provider can accomplish
the erasure either by sending an Erase Displayed Memory command or by
sending an Erase Non-Displayed Memory command followed by an End of
Caption command, effectively making a blank caption "appear".) Display
can also be erased by the receiver when the caption memory erasure
conditions are met, such as the user changing TV channels.

(11) Row: One of 15 horizontal divisions of the screen, extending
across the full height of the safe caption area as defined in paragraph
(n)(12) of this section.

(12) Safe caption area: The area of the television picture within which
captioning and text shall be displayed to ensure visibility of the
information on the majority of home television receivers. The safe
caption area is specified as shown in the following figure:
eCFR graphic ec03jn91.009.gif

View or download PDF

The dimensions of the above figure shall be as follows:
Label Dimensions Percent of television picture height
A Television picture height 100.0
B Television picture width 133.33
C Height of safe caption area 80.0
D Width of safe caption area 106.67
E Vertical position of safe caption area 10.0
F Horizontal position of safe caption area 13.33

(13) Special characters: Displayable characters (except for
"transparent space") which require a two-byte sequence of one
non-printing and one printing character. The non-printing byte varies
depending on the data channel. Regular characters require unique
one-byte codes which are the same in either data channel.

(14) Text: When written with an upper-case "T", refers to the Text
Mode. When written with a lower-case "t", refers to any combination of
displayable characters.

(15) Transparent space: Transmitted as a special character, it is a
one-column-wide space behind which program video is always visible
(except when a transparent space immediately precedes or follows a
displayable character and solid box is needed to make that character
legible).

[ 56 FR 27201 , June 13, 1991, as amended at 57 FR 19094 , May 4, 1992; 58 FR 44893 , Aug. 25, 1993. Redesignated and amended at 77 FR 19515 ,
19518, Mar. 30, 2012; 78 FR 39627 , July 2, 2013; 78 FR 77251 , Dec. 20,
2013]

Goto Section: 79.100 | 79.102

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