stas2k
DTACK Issue
On the schematic DTACK is Pin 1 on the GAL where as in the PLD file its is Pin 23. Since it is an output it can't be on Pin 1.
I noticed this after assembling a board with 3 SRAM chips and testing in an ACE with a Sharp 1 MB expansion on the internal memory expansion header. I worked around the issue by cutting the link on the "1 MB" jumper and adding a wire between the middle pad of the jumper and Pin 1 of the GAL. I tested with a program found somewhere called "mtest.r" which passed.
I also felt that the GAL was getting warm from driving DTACK as push-pull rather than open drain so I added an open drain buffer. It is maybe less warm, but I don't have a way to measure well. It worked with and without the buffer so this may not be an issue. I think using the tri-state outputs on the GAL should be able get the same effect.
On the schematic DTACK is Pin 1 on the GAL where as in the PLD file its is Pin 23. Since it is an output it can't be on Pin 1.
I noticed this after assembling a board with 3 SRAM chips and testing in an ACE with a Sharp 1 MB expansion on the internal memory expansion header. I worked around the issue by cutting the link on the "1 MB" jumper and adding a wire between the middle pad of the jumper and Pin 1 of the GAL. I tested with a program found somewhere called "mtest.r" which passed.
I also felt that the GAL was getting warm from driving DTACK as push-pull rather than open drain so I added an open drain buffer. It is maybe less warm, but I don't have a way to measure well. It worked with and without the buffer so this may not be an issue. I think using the tri-state outputs on the GAL should be able get the same effect.
Hi,
I assume then there might be an error on the current GAL routing and that fix you applied would be required if using 4 SRAM chips? As I mentioned on another issue I had no success with my built unit and I was blaming the GAL speed, but perhaps the problem is caused by this.
Thanks
Thanks for posting this fix. Looking at the PLD via WinCUPL Pin 1 (DTACK) isn't fused to anything internally anyway so tying it to MSK or NDTACK as its called in the PLD shouldn't do any damage. GAL's tend to run hot normally. I've had my Galspanic installed for 2 days and the GAL is warm to the touch.
Driving DTACK push-pull is likely to prevent other expansion cards from working that are installed alongside the RAM expansion. (It seems that this is currently accidentally being avoided by the DTACK line not being driven at all).
