HP 9845 C with 280 option startup failure

[Tequi Lizer]

Tony Duell wrote:
>> Here it is with relation to the boardswapper guides:
>>
>> NP/=MonAck/ --(  )-- WrFull/=FLB/
>>  NW/=MonStb --(  )-- DD15=GS
>>         Gnd --(  )-- MonClrAddr/=NL/
>>         Gnd --(  )-- +5V
>>    I6=MD(6) --(  )-- +5V
>>    CS=MD(7) --(  )-- +5V
>>    I4=MD(4) --(  )   N/C
>>    I5=MD(5) --(  )-- -Vm
>>    I2=MD(2) --(  )-- -Vm
>>    I3=MD(3) --(  )-- +Vm
>>    I0=MD(0) --(  )-- +Vm
>>    I1=MD(1) --(  )-- Gnd
>>    IV=MD(9) --(  )-- Gnd
>>   CUR=MD(8) --(  )-- MD(12)=RDA
>>   UL=MD(11) --(  )-- MD(13)=GRA
>>    B=MD(10) --(  )-- MD(14)=BLA
>> AS=GS/=DA14 --(  )-- Gnd
>>         Gnd --(  )-- Init/
>>
>> where
>>
>> NP = New Page (=> load start address + AS + GS from block 0 at address 
>> 600000 into address register
>>     
> )
>   
Here's a small typo, the frame buffer is located in block 1 (PPU memory).

>> NL = New Line (=> read one line from crt buffer into line buffer)
>> NW = New Word (=> provide next character+attribute data to monitor)
>>     
>
> Well, my names were'd too ridiculous, then, considering I worked them out 
> before seeing the boardswapper guide.
>
>   
>> AS = Alpha Select (=> enable alpha display, used as GS/ for switching 
>> between alpha and graphics on the monochromes)
>> GS = Graphics Select (=> enable graphics display on the 9845C only, 
>> where alpha & graphics can be displayed simultaneously)
>>     
>
> Are you sure that doesn't also apply to the 98780 enhanced mono monitor? 
> The text and graphic systems are pretty much seperate on that monitor, 
> OK, there is one video timing chain (on the text PCB) that provides 
> timing signals to the graphics board too, but the graphics unit has its 
> own memory, video shift register, etc. The outputs are combinded by a 
> fairly complex mixer circuit on the interface PCB in the monitor. There 
> is no good reason why the 2 can't be displayed at the same time.
>
>   
Maybe you're right. In fact, although (according to the boardswapper) 
the 98780 and the 98770 have slightly different overall video timings, 
both use one single scan raster for alpha & graphics with just different 
viewable areas. This is not the case for the standard mono crt. So maybe 
the parallel operation of alpha & graphics works for the 98780, too. The 
color crt enables both displays during initialization (CONTROL+STOP, 
thats what the INIT signal is for) and afterwards switches back to 
normal alpha only. Maybe the 98780 behaves in a similar manner.

However, I think I got all I need in order to make a first try for some 
substitute for the startup fixture. See how it works :-)


--Ansgar