Chapter 3

3.1 Controls

Two groups of controls are used in the VT52 Video Display Terminal, the operator controls and the keyboard. The operator controls set the operating parameters of the terminal such as parity, baud rate, etc. The keyboard keys select the codes to be transmitted to the host.

3.1.1 Operator Controls

The operator controls and their functions are listed in Table 3-1.

Table 3-1 Operator Controls
Control Location Function
ON/OFF Right side Applies power to the unit
Baud rate switches Front, bottom
S1-2 Full duplex with local copy*
S1-3 Full duplex*
S1-4 300 baud
S1-5 150 baud
S1-6 75 baud
S1-7 4800 baud
S2-A Match (Bell 103) -- Local Copy*
S2-B 110 baud
S2-C Match (Bell 103)*
S2-D 600 baud
S2-E 1200 baud
S2-F 2400 baud
S2-G 9600 baud
S3† Front, bottom Selects NO (mark) parity or EVEN parity (SPACE or ODD with jumpers)
Brightness Rear Sets screen intensity level
* In positions indicated with an asterisk, receiving and transmitting speeds will be the same. In other positions, S1 selects the transmitting speed and S2 selects the receiving speed. S1 and S2 switch positions 1A, 1C, 2A, 2C, 3A, and 3C are illegal.
Not user accessible, see the decal on the base for more information.

3.1.2 Keyboard

Input data to the host is entered by typing keys on the main keyboard or the auxiliary keypad (Figure 3-1). The keyboard transmits upper- and lowercase alphabetic code, numeric code, fixed control code, and user-defined control code. Alphabetic Keys -- All alphabetic keys transmit in uppercase and lowercase code. Uppercase is transmitted when a key is typed while either or both SHIFT keys are down or while the CAPS LOCK key is down. (The CAPS LOCK key does not affect codes transmitted by keys other than the alphabetic keys.) Upper- and lowercase codes are listed in Table 3-2.

Table 3-2 Alphabetic Key Codes*
Key Uppercase Code Lowercase Code
A 101 141
B 102 142
C 103 143
D 104 144
E 105 145
F 106 146
G 107 147
H 110 150
I 111 151
J 112 152
K 113 153
L 114 154
M 115 155
N 116 156
O 117 157
P 120 160
Q 121 161
R 122 162
S 123 163
T 124 164
U 125 165
V 126 166
W 127 167
X 130 170
Y 131 171
Z 132 172
* All codes are expressed in octal. Numeric/Symbol Keys -- Numeric and symbol keys codes are listed in Table 3-3.

Table 3-3 Numeric/Symbol Key Codes
Key Neither SHIFT
Key Down
Either or Both
SHIFT Keys Down
1 061 041 (!)
2 062 100 (@)
3 063 043 (#)
4 064 044 ($)
5 065 045 (%)
6 066 136 (^)
7 067 046 (&)
8 070 052 (*)
9 071 050 (()
0 060 051 ())
- 055 137 (_)
= 075 053 (+)
[ 133 135 (])
; 073 072 (:)
' 047 042 (")
, 054 074 (<)
. 056 076 (>)
/ 057 077 (?)
\ 134 174 (|)
` 140 176 (~)
{ 173 175 (}) Function Keys -- Function keys transmit control codes to the host. They cause an action to occur in the terminal such as tab, line feed, etc., if the host echos these codes back to the terminal. Table 3-4 lists the function keys, the code they transmit to the host, and the terminal action taken if the code is echoed back to the terminal.

Table 3-4 Function Key Codes
Key Code Action Taken if Codes Are Echoed
RETURN 015 Carriage Return function
LINE FEED 012 Line Feed function
BACK SPACE 010 Backspace (Cursor Left) function
TAB 011 Tab function
Space Bar 040 Deposit a space on the screen, erasing what was there before
DELETE 177 Nothing
ESC (SEL) 033 Interpret the next character from the host as a command, rather than displaying it The CONTROL Key -- The CONTROL key is used in conjunction with other keys on the keyboard to produce control codes in the range of 000-037. When held down, it alters the code normally produced by a typed key by forcing the two high-order bits of the code to zero. Table 3-5 lists the codes transmitted when the CONTROL key is held down. The original code is included for comparison.

Table 3-5 CONTROL Key Codes*
Name Transmitted Code Original Code
NUL 000 040 or 100 or 140
SOH 001 041 or 101 or 141
STX 002 042 or 102 or 142
ETX 003 043 or 103 or 143
EOT 004 044 or 104 or 144
ENQ 005 045 or 105 or 145
ACK 006 046 or 106 or 146
BELL 007 047 or 107 or 147
BS 010 050 or 110 or 150
HT 011 051 or 111 or 151
LF 012 052 or 112 or 152
VT 013 053 or 113 or 153
FF 014 054 or 114 or 154
CR 015 055 or 115 or 155
SO 016 056 or 116 or 156
SI 017 057 or 117 or 157
DLE 020 060 or 120 or 160
DC1 or XON 021 061 or 121 or 161
DC2 022 062 or 122 or 162
DC3 or XOFF 023 063 or 123 or 163
DC4 024 064 or 124 or 164
NAK 025 065 or 125 or 165
SYN 026 066 or 126 or 166
ETB 027 067 or 127 or 167
CAN 030 070 or 130 or 170
EM 031 071 or 131 or 171
SUB 032 072 or 132 or 172
ESC 033 073 or 133 or 173
FS 034 074 or 134 or 174
GS 035 075 or 135 or 175
RS 036 076 or 136 or 176
US 037 077 or 137 or 177
* The CONTROL key must be held down while typing the character key. The BREAK Key -- Typing the BREAK key forces the serial data output line of the terminal to the zero state for as long as the key is held down. The BREAK function is provided for users with software written to operate in half-duplex mode. Auxiliary Keypad -- The 19-key auxiliary keypad is provided for applications requiring heavy use of the numeric keys. In addition to the 10 numeric keys, the keypad has a decimal point key, 4 cursor move keys, 3 blank keys, and an ENTER key.

In normal mode the decimal point key and the numeric keys transmit the same code as the decimal point key and the numeric keys on the main keyboard; the host cannot distinguish between them. The ENTER key transmits the same code as the RETURN key.

When the ESC command = is typed on the keyboard, the terminal will enter the Alternate-Keypad mode and the ENTER, decimal point, and numeric keys will each transmit a unique Escape Sequence. This will allow the host to distinguish between main keyboard entries and auxiliary keypad entries. It also provides the host with 12 user-definable keys to use for his particular application. Table 3-6 lists the codes transmitted by these keys.

Table 3-6 Keypad Numeric Key Codes
Code(s) Transmitted To Host
Key VT52 not in Alternate-Keypad Mode VT52 in Alternate-Keypad Mode
0 060 033 077 160 (ESC ? p)
1 061 033 077 161 (ESC ? q)
2 062 033 077 162 (ESC ? r)
3 063 033 077 163 (ESC ? s)
4 064 033 077 164 (ESC ? t)
5 065 033 077 165 (ESC ? u)
6 066 033 077 166 (ESC ? v)
7 067 033 077 167 (ESC ? w)
8 070 033 077 170 (ESC ? x)
9 071 033 077 171 (ESC ? y)
. 056 033 077 156 (ESC ? n)
ENTER 015 033 077 115 (ESC ? M)

The seven remaining keys on the keypad are the four cursor move keys and three blank keys. The cursor move keys transmit an Escape Sequence to the host, and if the host echos these codes back to the terminal, the cursor will move one character position up, down, left, or right, depending upon the typed key. The three blank keys transmit user-defined Escape Sequences; the user can define the meaning of each key to fit his particular application. Table 3-7 lists the codes transmitted by these seven keys.

None of the keys on the auxiliary keypad are affected by pressing the SHIFT, CAPS LOCK, or CTRL keys.

Table 3-7 Keypad Control Key Codes
Keypad Key Codes Transmitted to Host
Blank (left) 033 120 (ESC P)
Blank (center) 033 121 (ESC Q)
Blank (right) 033 122 (ESC R)
Up-arrow 033 101 (ESC A)
Down-arrow 033 102 (ESC B)
Right-arrow 033 103 (ESC C)
Left-arrow 033 104 (ESC D) The REPEAT Key -- The REPEAT key is used in conjunction with other keys; it does not transmit a code. Any key that transmits a code to the host will transmit that code repeatedly if pressed while the REPEAT key is down. Keys that transmit more than one code will transmit their sequence repeatedly if pressed while the REPEAT key is down. The SCROLL Key -- The SCROLL key performs a local function; it does not transmit a code to the host. It is used to request more data from the host when the terminal is in Hold-Screen mode. Typing SCROLL will add one line of characters to the display screen; typing SHIFT SCROLL adds a screenful. The COPY Key -- The COPY key is also a local function key. When typed, the COPY key will produce a hard copy of the current screenful of characters, if the optional copier is installed.

3.2 Operating Procedure

3.2.1 Off-Line

Figure 3-2
Operator Control Switch Access Position
  1. Make certain that the terminal line cord is not connected to an electrical outlet and that the power (ON/OFF) switch is in the (OFF) position.
  2. Set the unit for OFF-LINE operation. To do this, set rotary switch S1 to position 1 and rotary switch S2 to position G. These switches are located at the front of the unit, under the keyboard. The unit will have to be tipped to the rear to gain access to the switches (Figure 3-2).
  3. Return the VT52 to its normal operating position and plug the line cord of the unit into an electrical outlet that meets the requirements of the terminal.
  4. Apply power to the terminal by setting the ON/OFF switch to ON. This switch is located on the right side of the terminal.
  5. After warmup (about half a minute) the flashing cursor will appear at the top left of the screen. This is called the HOME position.
  6. Using the brightness control located at the rear of the terminal (Figure 3-3), adjust the brightness of the cursor to the desired level. For the most comfortable viewing, set the brightness to the lowest possible level while still maintaining good character definition. High screen intensity causes characters to become fuzzy and prolonged viewing of the bright display is very tiresome.
    Figure 3-3
    VT52, Rear View
  7. Type a character. The character will appear on the screen at the cursor location and the cursor will move one character location to the right.
  8. With the REPEAT key held down, type another character. The character will appear in all the remaining locations of the top line and the cursor will be under column 79 (the last column).
  9. Type a different character. It will replace the last character in the line because that is the cursor location. The cursor advances automatically as characters are typed, until it reaches the last character position in the line. RETURN and LINE FEED must be typed at the end of each line.
  10. Type the RETURN key. The cursor will move to the left end of the line. Now type LINE FEED. The cursor will move down to the next line. Type a few characters to form the second line.
  11. Try the rest of the cursor move keys. They will all move the cursor one character position. The BACK SPACE key will move the cursor to the left; the four cursor move keys on the auxiliary keypad will move the cursor one character position in the direction indicated by the arrow.
  12. Move the cursor to the left-hand margin on a blank line. Alternately type a character and TAB. The typed characters will appear eight character locations apart. These are the TAB STOP locations. If the cursor is at the end of a line, TAB will not move the cursor.
  13. Position the cursor under a displayed character and type SPACE BAR. The character will be replaced with a space and the cursor will be advanced one character position. The space bar may be used for erasing.
  14. Type some characters with the SHIFT key and then the CAPS LOCK key held down. Alphabetic characters will appear in uppercase when typed with either SHIFT or CAPS LOCK pressed. Numeric keys are not affected when CAPS LOCK is held down. Symbols associated with the numeric keys are displayed only when the numeric keys are typed with the SHIFT key held down.
  15. Move the cursor to the left-hand margin of the bottom line. With REPEAT held down, type a character key and fill the bottom line. Type RETURN and LINE FEED. The terminal will move all lines UP by one position erasing the bottom line for new entries. The top line is lost in this operation. This is called scrolling and will occur whenever a LINE FEED is typed while the cursor is on the bottom line unless the terminal is in Hold-Screen mode.

3.2.2 On-Line

  1. Remove power from the terminal by switching the ON/OFF switch to OFF.
  2. Tip the unit up and set the baud rate switches to the desired frequency. Transmission speed must be set to the same frequency as the host's receiving speed; receiving speed must be set to the same frequency as the host's transmission speed.
  3. Return the VT52 to its normal operating position and set the ON/OFF switch to ON to restore power to the terminal. After warmup the terminal is ready for communication with the host.

3.3 User Maintenance

The keyboard and key-click mechanism are the only moving parts of the terminal and require no preventive maintenance by the owner. The DECscope may be cleaned with soap and water or any mild detergent. Although the terminal's shell provides superior resistance to damage from solvents, cleaners with solvents should not be used.

The DECscope packaging is not meant to be weatherproof; there are also several openings in the case through which liquids, coins, paper clips, and other objects can fall. Such objects will disturb the electronic operation of the terminal if they come in contact with the circuitry. For this reason, avoid putting drinks and metal objects on the top of the terminal, or using excessive water to clean the terminal. The keyboard area is an area where the electronics are particularly close to the exterior. Rubbing the keys with a dry or barely moist cloth should suffice to clean them. Do not remove the keycaps to clean them more thoroughly; damage may result to the switch contacts if they are replaced incorrectly.