4 Transmitted Characters

General

This chapter describes the characters generated by the VT102 keyboard. The keys are divided into three groups: standard keys, function keys, and numeric keypad keys.

Standard Keys

The keyboard generates American Standard Code for Information Interchange (ASCII) characters. The standard keys (Figure 4-1) generate lowercase ASCII characters when neither SHIFT or CAPS LOCK are down. These keys generate uppercase ASCII characters when either SHIFT or CAPS LOCK key are down. CAPS LOCK does not affect the nonalphabetic keys.

Figure 4-1 Standard Key Codes

Function Keys

The function keys (Figure 4-2) generate characters defined by the computer software or communication system. The following paragraphs describe the function keys.

Figure 4-2 Function Keys

BREAK/HERE IS

This key generates a break defined by the computer system when the break enable feature is on. This feature does not affect other key sequences using BREAK.

Hold down SHIFT and press BREAK to generate a long break disconnect. A long break disconnect usually disconnects the terminal from the communication line. See Break in Chapter 6 for more information about breaks and long break disconnects.

Hold down CTRL and press HERE IS to transmit the answerback message. See Chapter 3 for more information about the answerback feature.

Cursor Control Keys

In ANSI mode, with alternate (application) keypad mode selected, the cursor keys generate either application or cursor control sequences. Cursor key mode selects the type of sequence.

With numeric keypad mode selected, the cursor keys generate ANSI cursor commands. The computer selects both cursor key mode and keypad mode. See Cursor Key Character Selection in Chapter 5 for more information.

In VT52 mode, the cursor keys only generate VT52 cursor control sequences. Table 4-1 lists the ANSI and VT52 compatible cursor key characters.

Table 4-1 Cursor Control Key Codes
Cursor Key ANSI Mode VT52 Mode
Cursor Key Mode Reset Cursor Key Mode Set
ESC  [  A
033 133 101
ESC  O  A
033 117 101
ESC  A
033 101
ESC  [  B
033 133 102
ESC  O  B
033 117 102
ESC  B
033 102
ESC  [  C
033 133 103
ESC  O  C
033 117 103
ESC  C
033 103
ESC  [  D
033 133 104
ESC  O  D
033 117 104
ESC  D
033 104

Control Character Keys

Figure 4-3 shows the keys that generate control characters. You can generate control characters in two ways.

Table 4-2 lists the control characters generated by the keyboard. Different computer systems may use each control character differently.

NOTE: The VT102 generates some control characters differently than previous DIGITAL terminals. Table 4-3 lists the changes.

Figure 4-3 Function Key Control Codes
Table 4-2 Control Codes Generated
Control Character Mnemonic Transmitted Code (Octal) Key Pressed with CTRL Dedicated Key
Null NUL 000 Space Bar -
Start of heading SOH 001 A -
Start of text STX 002 B -
End of text ETX 003 C -
End of transmission EOT 004 D -
Enquire ENQ 005 E -
Acknowledge ACK 006 F -
Bell BEL 007 G -
Back space BS 010 H BACK SPACE
Horizontal tabulation HT 011 I TAB
Linefeed LF 012 J LINE FEED
Vertical tabulation VT 013 K -
Form feed FF 014 L -
Carriage return CR 015 M RETURN*
Shift out SO 016 N -
Shift in SI 017 O -
Data link escape DLE 020 P -
Device control 1 DC1 (XON) 021 Q -
Device control 2 DC2 022 R -
Device control 3 DC3 (XOFF) 023 S -
Device control 4 DC4 024 T -
Negative acknowledge NAK 025 U -
Synchronous idle SYN 026 V -
End of transmission block ETB 027 W -
Cancel of previous word or character CAN 030 X -
End of medium EM 031 Y -
Substitute SUB 032 Z -
Escape ESC 033 [ -
File separator FS 034 \ -
Group separator GS 035 ] -
Record separator RS 036 ~ -
Unit separator US 037 ? -
Delete DEL 177 DELETE
* The numeric keypad mode determines whether RETURN and ENTER generate the same control codes. The codes generated by RETURN are changed by two feature selections:
  • The auto turnaround SET-UP feature when using half-duplex coded control (HDX B). The turnaround/disconnect SET-UP feature selected the turnaround character. If the turnaround character is carriage return (CR), the terminal transmits only one CR when you press RETURN.

  • The line feed/new line feature. When this feature is on, RETURN generates two characters (CR, LF). When this feature is off, RETURN generates a CR.

Table 4-3 VT102 Key Changes
Control Code VT102 Previous Terminals
NUL (octal 000) CTRL Space Bar CTRL @
RS (octal 036) CTRL ~ CTRL ^
US (octal 037) CTRL ? CTRL _

Numeric Keypad Keys

These keys generate characters selected by the ANSI/VT52 feature and alternate (application) keypad mode. The computer selects application keypad mode. See Keypad Character Selection in Chapter 5 for more information.

In numeric keypad mode, the numeric keypad generates the numeric, comma, period, and minus sign characters used by the main keyboard. In application keypad mode, the numeric keypad generates control functions. Table 4-4 lists the characters generated by the numeric keypad.

Table 4-4 Keypad Codes
Key ANSI Mode VT52 Mode
Numeric Keypad Mode Application Keypad Mode Numeric Keypad Mode Application Keypad Mode
0 0
060
ESC  O   p
033 117 160
0
060
ESC  ?   p
033 077 160
1 1
061
ESC  O   q
033 117 161
1
061
ESC  ?   q
033 077 161
2 2
062
ESC  O   r
033 117 162
2
062
ESC  ?   r
033 077 162
3 3
063
ESC  O   s
033 117 163
3
063
ESC  ?   s
033 077 163
4 4
064
ESC  O   t
033 117 164
4
064
ESC  ?   t
033 077 164
5 5
065
ESC  O   u
033 117 165
5
065
ESC  ?   u
033 077 165
6 6
066
ESC  O   v
033 117 166
6
066
ESC  ?   v
033 077 166
7 7
067
ESC  O   w
033 117 167
7
067
ESC  ?   w
033 077 167
8 8
070
ESC  O   x
033 117 170
8
070
ESC  ?   x
033 077 170
9 9
071
ESC  O   y
033 117 171
9
071
ESC  ?   y
033 077 171
- - (minus)
055
ESC  O   m
033 117 155
- (minus)
055
ESC  ?   m
033 077 155*
, , (comma)
054
ESC  O   l
033 117 154
, (comma)
054
ESC  ?   l
033 077 154*
. . (period)
056
ESC  O   n
033 117 156
. (period)
056
ESC  ?   n
033 077 156
ENTER CR or CR LF
015 or 015 012
ESC  O   M
033 117 115
CR or CR LF
015 or 015 012
ESC  ?   M
033 077 115
PF1
ESC  O   P
033 117 120
ESC  O   P
033 117 120
ESC  P
033 120
ESC  P
033 120
PF2
ESC  O   Q
033 117 121
ESC  O   Q
033 117 121
ESC  Q
033 121
ESC  Q
033 121
PF3
ESC  O   R
033 117 122
ESC  O   R
033 117 122
ESC  R
033 122
ESC  R
033 122
PF4
ESC  O   S
033 117 123
ESC  O   S
033 117 123
ESC  S
033 123
ESC  S
033 123

* These sequences are not generated by the VT52 terminal

† In numeric keypad mode (application keypad mode off), you can change the ENTER character code with the linefeed/new line feature. When off, this feature causes ENTER to generate a single control character (CR, octal 015). When on, this feature causes ENTER to generate two characters (CR, octal 015 and LF, octal 012).