Closed SRAM for C64
- Thread starter plazma
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They fit motherboard revisions 250466 & 250469. A C64C model usually got the 469 short motherboard. But it may also have any other board. If it got a long board it usualy is 425 or 466.
Available again. New 1.1 version. Or-gate replaced with inverter-gate.
This version have proven to work well with bot 466 & 469 version motherboards.
Customers have replaced other SRAM boards with this and 466 started working.
This version have proven to work well with bot 466 & 469 version motherboards.
Customers have replaced other SRAM boards with this and 466 started working.
D
Deleted member 14264
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The real problem is the SRAM IC. People who don't pay attention to electronics details use a 12ns SRAM IC and these very fast IC don't like slow transition signals generated by antique 1MHz computers.
The solution is to use slower RAM rated for 45-70ns.
Yes only 466 boards. My 1.0 desing worked well with 466 anyway. Jamarjus design at github failed and my design worked with the same motherboard. I asked buyers for motherboard revision so I can follow compatibility.
D
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Jamarjus design has multiple issues.
1. The OR gate was a 74F32 in the original design - excessive power and too fast. Recommended replacement is a single gate 74HCT1G32.
2. This design uses ground pins in a very irresponsible way as it forces you to desolder all 4 ground pins and uses the Output Enable function of the DRAM which are simply tied to ground on the C64/C64c.
3. He used a 12ns high speed cache SRAM IC which is very sensitive to the slow transition signal of old 8 bit computers and this causes write errors. This makes this design unreliable. The fix is to use a slower 45ns/55ns IC which uses less power and correctly takes slower signals. This problem is more prevant on the 250466 because it uses legacy 74LS technology to manage the multiplexed address bus. The 469 uses the large 64 pin PLA which uses HMOS/CMOS technology and has sharper transitions.
4. There is no need for all the pins as you can take advantage of the redundancy of address and control lines on both DRAM footprints helping make the board much smaller.
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Coming soon: the new model called neatSRAM.
Fits all C64 motherboards. Designed to have a neat install also in 8 DRAM chip motherboards.
Totally new design with logic emulating the original DRAM better than older designs.
Fits all C64 motherboards. Designed to have a neat install also in 8 DRAM chip motherboards.
Totally new design with logic emulating the original DRAM better than older designs.
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