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Old 8th Jul 2019, 5:47 pm   #142
john_newcombe
Hexode
 
Join Date: Apr 2019
Location: Skipton, North Yorkshire, UK.
Posts: 252
Default Re: Gemini 80-Bus System

More like mud than concrete....

First I programmed up a ROM with Neal's code designed to test IC25.

Code:
        ld hl, 0xc000           ; status write 
loop:   ld (hl), a              ; write
        inc a
        jr loop
I checked the outputs of IC25, pins 2,16,19 showed a square wave with some 'glitchiness'. On the others, a more sinusoidal waveform of a higher frequency.

I then programmed up a rom to test the dot clock e.g.

Code:
        ld hl, 0xc000           ; status write 
        ld a, 0x02              ; crystal dot clock
        ld (hl), a              ; write
loop:   jr loop
With the above code, it was necessary to reset the CPU many times (10+) before I saw pin 9 of IC25 go high and select the 16Mhz Xtal dot clock. This seems to be the case at each power up.

I have little idea of what this all means as yet....

Next up is to check the reset via port B3, the code I have to do this is as per John e.g.

Code:
loop:   in  a,($b3)
        out ($b3),a
        jr loop
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