DEC VT220 Technical Manual page 158

To send a peripheral command, set the TYPE flag (low order bit).
Bits six -- three contain a command representation from the chart
below. Bits two and one specify on (01), off (00), or sound (11).
Bit seven should be set if there are no parameters to follow.
Table
7-4
lists the peripheral commands (in hexadecimal).
Table 7-4 Peripheral Commands
in
Hexadecimal
Function
Flow control
Resume keyboard transmission
Inhibit transmission
Indicators
Light LEDs
Turn off LEDs
Audio
Dis ble lick
Enable clic , set olume
Disable CTRL keyclick
Enable CTRL k 1 ck
So lick
Disable 11
Enable bell, set volume
Sound bel
Autor
t
Temporary autorepeat inhibit
Enable autorepeat across keyboard
Disable autorepeat across keyboard
Change a 1 aut or t to down only
Other
Request keyboard ID
Jump to powerup
Jump to test mode
Reinstate defaults
7-32
Hex
8B
89
13
11
99
IB
B9
BB
9F
Al
23
A7
Cl
E3
El
D9
AB
FD
CB
03
Parameters
None
None
Bit pattern
Bit pattern
None
Volume
None
None
None
None
Volume
None
None
None
None
None
None
None
None
None