Author
| Is the V9938 compatible with SRAM ?
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Gsparis
msx friend
Posts: 4 |  Posted: March 08 2007, 10:33 |
Hi Everyone,
I recently managed to get some V9938 VDP chips and am thinking about making a graphic card for a personal project based on a Z80 architecture.
Since now 80's static RAM chips in DIL package are cheap and still easy to get I would like to use 128Kb single SRAM chip (easy to implement in a design and in a PCB) instead of DRAM chips.
So my question is:
Does the V9938 VDP chip compatible with SRAM only RAM chips and if so, is there any specific ways of connected the VDP chip to the SRAM chips ?
Thanks in advance for the people who will reply.
Gsparis
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PingPong
msx professional
Posts: 869 | Posted: March 08 2007, 14:41 |
look at the yamaha datasheet
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Gsparis
msx friend
Posts: 4 | Posted: March 08 2007, 15:18 |
Hi PingPong,
Sorry, I should have written that I already read the datasheet about the V9938.
Unfortunately, this datasheet only lists implementations with various DRAM chips.
My question relates to SRAM chips only.
It's because I'm not 100% confident that all I have to do to make it work is just replace DRAM chips by SRAM chips and connect the latter's pins to the VDP that I'm asking for some help or at least confirmation that that's all I have to do !
Gsparis
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flyguille
msx master
Posts: 1182 | Posted: March 08 2007, 19:42 |
with SRAM works for sure.... include is capable to disable the REFRESH cycle with SRAM!
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Gsparis
msx friend
Posts: 4 | Posted: March 08 2007, 23:25 |
Quote:
| include is capable to disable the REFRESH cycle with SRAM!
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Sorry I don't understand what your mean by that ?
What is "include" ?
Gsparis |
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jltursan
msx professional
Posts: 826 | Posted: March 08 2007, 23:50 |
I guess that flyguille is trying to tell you that using SRAM you can even disable the refresh cycle needed by the DRAM memory
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DamageX
msx freak
Posts: 162 | Posted: March 09 2007, 02:29 |
looks like you will need to latch the address bits 8-15 when RAS goes low
connect (/CAS0 AND /CAS1) to /OE on the SRAM and use one of them for A16 also
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flyguille
msx master
Posts: 1182 | Posted: March 09 2007, 03:51 |
IIRC the vdp has a bit register that if you reset it, the VDP turn off de refresh cycle. (atleas in MSX1's vdp)... so, on a normal MSX1 that means all data gone.... IIRC that also means a terribly hung at BASIC's prompt I really don't know why..... ¿maybe the register table also is erased without refresh?
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Gsparis
msx friend
Posts: 4 | Posted: March 09 2007, 08:37 |
Flyguille, I re-read the datasheet of the V9938 but I don't see anything about the disabling of the refresh function.
I will check this on the V9918. Maybe it does exist but isn't documented so the V9918 datasheet might be of help.
DamageX, you're right !
I need to demultiplex the data bus (I guess with a 74HC373 octal latch IC) in order to get the misssing A8-A15 address bits with the help of CAS0 or CAS1 (I need to check which of them must be used as /OE and A16).
Also, it seems I need to adjust VR to get a straight A8-A15 correspondance from the demultiplexed data bus AD0-AD7.
If anybody knows any details, I'd be grateful to share your knowledge.
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