WDI-II weirdness

[Christopher Mallery]

Anyone ever encountered the CPU not finding ROM with a WDI-II plugged in.

System is a Z-2 with a ZPU, 256KZ and 16FDC.  Everything works fine until I plug in this WDI-II.  What I can see with a Jade Bus Probe card is that the ZPU seems to make the jump to C000 and I have tested that ROM starts to run with a HALT ROM, but without the HALT ROM within a second the Address lines start counting/searching memory like it lost contact with the ROM.  My current theory is that WDI's 244 buffer on the data lines got borked somehow.  I will get around to testing ICs, but the board doesn't have sockets so I am not looking forward to that project.  Wondering if anyone else has any ideas.

Thanks,

Chris

[Jay Cotton]

I have never run that board but I suspect phantom* may be the issue.  i.e. the wdi board has a rom on board and perhaps its getting to the

bus.  Or perhaps the data bus is stuck on and the wdi is pounding the bus.

just some ideas

jc

[Mike Arnold]

Your theory of a bus buffer is a good possibility.

I could also suggest that you try the simple things first. I think that your ZPU and 16FDC will be socketed. Cromemco had a problem with chips in sockets so I would do a chip clean/reseat on all the chips to eliminate that. The WDI-II has two characteristics not seen on your other boards. Firstly, it has DMA so you could check the BUSRQ and BUSAK lines to ensure that the DMA chip has not been triggered. Also, the WDI-II has an 8 bit address register to allow 24 bit addressing for DMA. It is possible that this might interfere with the lower 16 bits if there is a hardware fault. You might check if there have been any non-Cromemco mods made to the WDI-II. 

Best of all, borrow another known working WDI-II to narrow down the culprit.

If you really run into a brick wall and are convinced that it is the WDI-II you could send it to me (UK) and I will look at it. However, I don't know if import tariffs will be triggered by sending boards between the States and UK though? 

[Christopher Mallery]

I will check the ZPU board, but I swapped it with another ZPU and showed the same symptoms.  I even swapped out the 256kz with a set of 16kz boards and the 16fdc with a 4fdc and all combinations of those show the same problem.  So I am pretty sure it's the wdi causing the issue,  but i will reseat everything because it can't hurt :)

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[Christopher Mallery]

The plot thickens.  I verified that the DMA line on the WDI is not active during the faulty behavior (i.e. low) so I don't think DMA is the culprit.

Next I decided to take my HALT ROM and just add a tight loop at C000 to see if the fault just appears after ROM begins to read on its own or RDOS is doing something to trigger the fault.  Turns out the fault doesn't appear with the tight loop.  So something in this chunk of code below.  Its not really doing anything that special.  Its just cycling through the baud rates until it sees a CR.  I guess the next step is to use HALT or my loop to find which instruction triggers the fault.  I am glad I have a lot of 2708s, lol.

STAT:   EQU     0       ;STATUS PORT
DATA:   EQU     1       ;DATA PORT
COMMND: EQU     2       ;COMMAND PORT
BAUD:   EQU     0       ;BAUD RATE PORT
DAV:    EQU     40H     ;DATA-AVAILABLE MASK

; BAUD RATES:
; 19200, 9600, 4800, 2400, 1200, 300, 150, 110.
;
BAUDRS: DEFB    90H,0C0H,0A0H,90H,88H,84H,82H,1

;CHECK INPUT & RETURN WITH DATA IF READY
;
CHKIN:  IN      A,(STAT)
        AND     DAV
        RET     Z
        IN      A,(DATA)
        RET
;
;
; GET CHARACTER FROM INPUT.
;
GBYTE:  CALL    CHKIN
        JR      Z,GBYTE
        AND     7FH
        RET

INITBAUD: LD    HL,BAUDRS
        LD      C,BAUD
        LD      A,19H           ;OCTUPLE THE CLOCK
IT1:    OUT     (COMMND),A      ;& RESET CURRENT DEVICE
        OUTI
        CALL    GBYTE
        CALL    GBYTE
        CP      CR
        LD      A,9             ;SLOW THE CLOCK
        JR      NZ,IT1
        RET

[Christopher Mallery]

Through the creative use of kapton tape and my logic analyzer the WDI card is pegging DO6 high.  Now where in the heck did I put my LS245s, lol.

[Mike Stein]

Almost there; congratulations!

What kind of drive are you using?

m

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[Christopher Mallery]

I am actually working on an IMI7710 emulator.  I have it mostly working, just a few bugs to work out.

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[Mike Stein]

You need to get in touch with Mike Arnold; he's working on a WDI-II emulator ;-)

To view this discussion visit https://groups.google.com/d/msgid/cromemco/CAPKaxwJVMgzbyMiDAigkkNcftA4dmYe3R6GqGgzvxarhpWmOMw%40mail.gmail.com.

[Christopher Mallery]

Yes, we have compared notes!

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