41
The Line Printer Controller state contains these registers:
Name Size Radix Symbolic Read-Only Action
BUF
16 8
Output buffer
STA
16 8 Printer status
POWER
28
Printer power state
CTL
1 2 Control flip-flop
FLG
1 2 Flag flip-flop
FBF
1 2 Flag buffer flip-flop
CCNT
7 10 Current character count
LCNT
7 10 Current line count
POS
32 10 Printer file position
CTIME
24 10 Character transfer time
PTIME
24 10 Per-zone print operation time
STIME
24 10 Per-line paper slew time
RTIME
24 10 Power-on ready delay time
The BUF register may be displayed in character format, if desired. Symbolic entry is also supported.
4.7 12792C 8-Channel Asynchronous Multiplexer
The 12792C is an eight-channel asynchronous serial multiplexer that connects terminals, modems, serial line
printers, and "black box" devices that use the RS-232 standard to the CPU. It uses an on-board Z80
microprocessor and provides input and output buffering to support block-mode reads from HP 264x and 262x
terminals at speeds up to 19.2K baud. The interface handles character editing, echoing, ENQ/ACK handshaking,
and read terminator detection, substantially reducing the load on the CPU over the earlier 12920A multiplexer.
There are four major revisions to the multiplexer firmware, designated revisions A-D. Revisions A-C have an
upward-compatible command set and are supported under RTE-M, RTE-IVB, and RTE-6/VM. Revision D
implements completely different commands, requires different RTE drivers, and is supported only under RTE-6/VM.
This simulation implements revision C.
Revisions B and C added support for the 37214A Systems Modem subsystem and the RTE-A Virtual Control Panel
(VCP), as the same firmware was used in the A-Series version of the multiplexer, the HP 12040B/C. Under
simulation, the modem commands return status codes indicating that no modems are present, and the VCP
commands are not implemented.
After pressing the CPU front-panel PRESET button or executing a CLC 0 instruction, the multiplexer enters
“echoplex” mode. In this mode, each channel defaults to 9600 baud, 8 bits per character, 1 stop bit, no parity, and
echoes characters as they are received. Echoplex is implemented under simulation — until a channel is configured
by the appropriate RTE driver control call, characters entered in a Telnet session will be echoed.
The 12792C has two baud-rate generators that are assigned to channels by the wiring configuration in the I/O cable
connector hood. Two counter/timer circuits on the interface are used to implement the BRGs for all eight channels.
For channels connected to the same BRG, only subsets of the configurable rates are allowed, and assigning
mutually incompatible rates causes corruption of the rates on channels assigned earlier. Under simulation, any
baud rate may be assigned to any channel without interaction.
While the multiplexer can connect to generic Telnet clients, RTE programs generally assumed the use of HP
terminals.
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