bitfixer
Veteran Member
Hi,
I'm wondering if anyone can help me to understand the difference between two SRAM chips in a piece of support hardware I'm building.
I've recently designed a board I'm calling the PETvet which is a RAM/ROM replacement for a Commodore PET. It connects to the 6502 socket in the pet and uses a single SRAM chip on the board to replace all of the RAM and ROM on the original PET motherboard.
Here's what is a bit confusing to me. In my initial design, I used a Hitachi 628128 SRAM chip (http://www.futurlec.com/Memory/628128.shtml), which has been working fine. In an attempt to lower the overall cost of the kit, I ordered a few Alliance AS6C1008 (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.alliancememory.com%2Fpdf%2FAS6C1008%2520feb%25202007.pdf&ei=2mwPT7H-PKOriAKs5dHSDQ&usg=AFQjCNEuDd3ACHGShMFBJQhmZ51sBBvLdg), which were quite a bit cheaper.
While the Alliance chip has the same pinout, and actually has a faster access time (55ns vs 70ns), the PETvet just doesn't work with the Alliance chip. When using it only as a RAM replacement, I see strange garbage written into memory, and when used as a ROM replacement as well the PET does not boot properly. I'm assuming that some subtlety of the chips is different enough that one works in the design while the other does not..
If anyone cases to take a look, please let me know if you see any obvious/significant differences between the chips. In the meantime I'll just use the more expensive hitachi chip in the design.. Thanks!
- Mike
I'm wondering if anyone can help me to understand the difference between two SRAM chips in a piece of support hardware I'm building.
I've recently designed a board I'm calling the PETvet which is a RAM/ROM replacement for a Commodore PET. It connects to the 6502 socket in the pet and uses a single SRAM chip on the board to replace all of the RAM and ROM on the original PET motherboard.
Here's what is a bit confusing to me. In my initial design, I used a Hitachi 628128 SRAM chip (http://www.futurlec.com/Memory/628128.shtml), which has been working fine. In an attempt to lower the overall cost of the kit, I ordered a few Alliance AS6C1008 (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.alliancememory.com%2Fpdf%2FAS6C1008%2520feb%25202007.pdf&ei=2mwPT7H-PKOriAKs5dHSDQ&usg=AFQjCNEuDd3ACHGShMFBJQhmZ51sBBvLdg), which were quite a bit cheaper.
While the Alliance chip has the same pinout, and actually has a faster access time (55ns vs 70ns), the PETvet just doesn't work with the Alliance chip. When using it only as a RAM replacement, I see strange garbage written into memory, and when used as a ROM replacement as well the PET does not boot properly. I'm assuming that some subtlety of the chips is different enough that one works in the design while the other does not..
If anyone cases to take a look, please let me know if you see any obvious/significant differences between the chips. In the meantime I'll just use the more expensive hitachi chip in the design.. Thanks!
- Mike