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Re: A bug in i8275 emulation [Re: fulivi] #112832
03/10/18 06:18 PM
03/10/18 06:18 PM
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R. Belmont Offline
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In that case I'd guess the 8275 only sees every other byte - that's easy enough to pull off at a hardware level. Are there schematics?

Re: A bug in i8275 emulation [Re: fulivi] #112834
03/10/18 06:41 PM
03/10/18 06:41 PM
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shattered Offline
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Re: A bug in i8275 emulation [Re: fulivi] #112835
03/10/18 07:28 PM
03/10/18 07:28 PM
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That is weird, two 8275s but only one is connected to the chargen. The way it's wired up does suggest that the second handles char attributes. Strangely though, the data fed by the dmac is the same to both except the topmost bit of the second crtc. That's not quite right, although the second crtc doesn't connect the drq output and the data lines (other than bit 7) are the same, the WR line is different when dack is active.

Last edited by crazyc; 03/10/18 08:18 PM.
Re: A bug in i8275 emulation [Re: fulivi] #112836
03/10/18 08:26 PM
03/10/18 08:26 PM
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So the first one (DD55) is not getting data via DMA, only second one does? Fun smile

Re: A bug in i8275 emulation [Re: fulivi] #112837
03/10/18 08:35 PM
03/10/18 08:35 PM
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Not sure but I suspect it is by feeding the second one first so the first one will hold drq high until both get a byte.

Re: A bug in i8275 emulation [Re: fulivi] #112838
03/10/18 09:59 PM
03/10/18 09:59 PM
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shattered Offline
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There's a bit of source code in the rom at the end (comments by me):
Code
CALL pEPEdA~A ; transmit
RET
KTO:
LXI H,bufp
SHLD Tp
KTO1:
CALL ANBUF
LDA FN
ANI 1
JNZ zb4
LDA zHp2
CPI 0


and it matches this

Code
2bbc: cd 78 19  call $1978
2bbf: c9        ret
2bc0: 21 28 df  lxi  h,$df28
2bc3: 22 25 df  shld $df25
2bc6: cd 89 2d  call $2d89
2bc9: 3a 05 de  ldax $de05
2bcc: e6 01     ani  $01
2bce: c2 72 26  jnz  $2672
2bd1: 3a 4c df  ldax $df4c
2bd4: fe 00     cpi  $00

Re: A bug in i8275 emulation [Re: fulivi] #112843
03/11/18 10:46 AM
03/11/18 10:46 AM
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shattered Offline
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btw, EAROM hookup is currently wrong -- top 4 bits of data bus are wired to CS, /WR, /ERA and RD pins. 0x08D9 is EAROM restore routine and 0x1F8D is EAROM save.

EDIT: quick EAROM hack makes the terminal behave a little better -- it accepts serial port input, but still ignores keyboard and display is not stable:

[Linked Image]

Last edited by shattered; 03/11/18 02:18 PM.
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