HP 9845 C with 280 option startup failure

Tony Duell ard at p850ug1.demon.co.uk
Tue Nov 8 15:44:47 CST 2005


> >   
> Yes, and they implemented the whole control logic in TTL (ROM based 
> state machine). The state machine is one of the more complex works, 
> since it uses both ROM tables and 16-bit multiplexer and a couple of 

IT's not as bad as it looks. The 2 ROMs form a 16 word * 13 bit table (3 
outputs of U34, 1816-1397 are not wired, the A4 input of both ROMs is 
tied to logic 0).

The ROMs are addressed by a '163 counter. It can be parallel loaded from 
4 of the ROM outputs, the load is controlled by that '150, the select 
inputs of that are the same signals as the ROM address lines.

> gates/counters/latches. Maybe the multiplexer is used primarily for the 
> access control of the PPU bus. I'm currently looking for the signal 
> lines between the board and the CRT. Besides the 15 character 
> code/character attribute lines and the power lines there are up to 7 


OK, here's a pinout from the schematic.

            Rear of machine, looking down into the edge connector
            on the 98770-66534 board

  MonAck/ --(  )-- WrFull/
   MonStb --(  )-- DD15
      Gnd --(  )-- MonClrAddr/
      Gnd --(  )-- +5V
    MD(6) --(  )-- +5V
    MD(7) --(  )-- +5V
    MD(4) --(  )   N/C
    MD(5) --(  )-- -Vm
    MD(2) --(  )-- -Vm
    MD(3) --(  )-- +Vm
    MD(0) --(  )-- +Vm
    MD(1) --(  )-- Gnd
    MD(9) --(  )-- Gnd
    MD(8) --(  )-- MD(12)
   MD(11) --(  )-- MD(13)
   MD(10) --(  )-- MD(14)
     DA14 --(  )-- Gnd
      Gnd --(  )-- Init/

Where : 
+Vm = +18V monitor supply from mainframe PSU
-Vm = -18V monitor supply from mainframe PSU

DA14, DD15 are 2 blanking/control signals (derrived, sortof, from address 
14 and data 15), mainframe to monitor
 
Init/ = mainframe reset signal (to monitor)

MocAck/ = Vertical timing signal from monitor text PCB

MonStb = Charater strobe from monitor text PCB

WrFull/ = Buffer full (to monitor text PCB)

MonClrAddr/= Clear buffer memory address (end of line) from monitor text PCB

MD(n) = 15 bit date word to monitor text PCB

   0...6 == Ascii code
   7 = chracter set seelct (or alternatively, 0..7 = character code :-))
   8 = cursor at this location
   9 = inverse video
  10 = blink
  11 = underline
  12..14 = colour select (not used on mono monitor)

You really need the schematics :-)

For reference the other monitor connector, on the 09845-69555 Printer 
Driver PCB is just the PPU I/O bus : 

   Rear of machine, looking down into connector

  PA(2) --(  )-- +5V
  PA(3) --(  )-- +5V
  PA(0) --(  )-- +12V  
   STS/ --(  )-- -12V
  PA(1) --(  )-- Flg/
  DMAR/ --(  )-- Dout/
  IOSB/ --(  )-- Gnd
   IRH/ --(  )-- Gnd
  IC(1) --(  )-- IOD(1)
   Int/ --(  )-- IOD(0)
  IC(2) --(  )-- IOD(3)
IOD(14) --(  )-- IOD(2)
IOD(15) --(  )-- IOD(5)
IOD(12) --(  )-- IOD(4)
IOD(13) --(  )-- IOD(7) 
IOD(10) --(  )-- IOD(6)
IOD(11) --(  )-- IOD(8)
    Gnd --(  )-- IOD(9)

Where the signals are just unbuffered versions of the signals on the I/O 
slots (same as a 9825, for example).
   
> lines which are dedicated for status/control information. You say there 
> are 3 lines which are not connected to the 98780 monitor backplane, can 
> you tell me which they are or anything about the estimated purpose of 
> the lines you found?

Is the above of any help?

-tony



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