CAS signal in SVI 738 or MSX in general

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By alexito

Hero (522)

alexito's picture

04-07-2019, 00:48

Good job lkpalwa, I looking forward for more tips about this great MSX machine. keep the good work and good luck.

P.S: I got a SVI-738 while ago and I just made the mod for the VRAM upgrade.

By LS120

Expert (95)

LS120's picture

26-07-2019, 11:35

what mod was that? and IKPALWA do you have anything in circuit diagram for the mapper?

thanks and good work

By lkpalwa

Expert (85)

lkpalwa's picture

22-08-2019, 16:15

Some Input, good news is thas /CAS and /RAS works as expected with 64x1 (8 chips original) and also with 64x4 (2 chips) .. there where some issues with /RD signal depending where is take from TP5 is inverted /RD and chips ned just RD to works as the /WE signal, Sorry @Nyyrikki but the A0 to A15 (LS30 plus LS32) do not solve the issue with remapping slots.
So the issue I have now is to make a slot select that handle 3-3 and 3-2, question if ULA chips just handle 3-0 and 3-1.
Looking as Schematics and also reading some info in WIKI about slots we need to have D0-D7 + A0-A1 and A14, A15, i also compare some schematics from other source and almost all are using the TTL LS273, LS153 and LS139.
I was little confused about replace the ADDRESSOUT (PIN 40 on ULA IC52), I think the problem is pins 44, 43 becasue signal out from PIN 40 in ULA is just used to enable LS139 and get SLTREG signal into ULA, IC63 have as I can see 4 state
3-0 to 3-3 and does are handle by A/B singal from EXPSLTA/EXPSLTB
LL 3-0
HL 3-1
LH 3-2
HH 3-3
Question if the two last are not implemted in code for ULA or is that maybe control by what BIOS send in D0-D7, A0,A1, A14, A15 and A6 into ULA ? I look into ULA all signal in incl Dx lines is almost same as need in for example Expert2/Expert3 and also Japanis docs in MSX Datapack for creating the SLT30 to SLT31, almost same based on the LS273 (Octal D-type Flip-Flop ) and LS153 (DUAL 4-INPUT MULTIPLEXER) to make A/B signal to LS139 and generate the 3-0 to 3-3

So any inputs from any HW experts how to generate the SLT3-2 and SLT3-3, I also have understand that the FFFF signal in SVI738 is not correct, where can I find that info?

Thx in advanced

By lkpalwa

Expert (85)

lkpalwa's picture

22-08-2019, 16:37

LS120 here is the embryo to mapper, as I say its not 100% working as we need to solve the SL3-x issues, as soon I got that fixed I wll prepare PCB boards at selfcost, I will replace TTL with CPLD to minimize build area

https://imgur.com/a/2wZUdXD

By lkpalwa

Expert (85)

lkpalwa's picture

05-09-2019, 20:26

so conclusion is that if you just use to chips, the provided CAS signal from ULA chip works, I have replace the 64x1 dram (8 chips) with 64x4 (2 chips), and looking at the mapper for NMS8250 (orginal with 128KB) the solve that by using the D2 singal togeather with /CAS E signal and 74LS32 + 74LS04, that will be active for both if /CAS_E HIGH then /CAS1 and /CAS2 are high and if D2 is HIGH then /CAS1 is HIGH and /CAS2 is LOW, and the opposite if D2 is LOW.

So /CAS isssue is solved, still working on setting memory to slot 3-3, that should be possible I got some images from Skjoldhammer and a link to a MSX2+ with 1MB, as I can see on those images they use the SLT33 (PIN 7 on 74LS139 IC63)

Mapper 1MB

I will open a new theard in HW to see if I can with some help get the mapper logic to work, I think I have almost all there now but have some questions about back annotion and the differense of expert2 and the NMS8250 mapper, specially A7' and /RESET logic in that design :-? :-? :-? :-?

By lkpalwa

Expert (85)

lkpalwa's picture

05-09-2019, 20:27

So to be clear the post 22-08-2019 will not work, because of missing of back annotation logic Sad
So DO NOT USE that Wink Wink Wink

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