Tiger wrote: ↑Sun Nov 07, 2021 1:16 pm
Note from the service-manual: All RAM chips should have 150ns access time and 128 row refresh.
Not all 4164 or equivalent DRAM chips are the same (and the various manufacturers used various numbers/codes). Two very important points:
- The chosen chip has to have an access time that is fast enough, otherwise strange and weird problems will occur.
- The refresh has to be the correct type. See below.
There are two memory layouts in this DRAM chip size. Both have exactly the same pin-out. All are 64k bit (65536 bit) in size.
One has a memory cell matrix of 8 x 8 and requires a 256 cycle refresh address. These are not compatible with a Z80, as it only has a 7 bit (128 cycle) refresh system.
You need the other type. These chips that have a 7 x 9 matrix and hence use a 128 cycle refresh address. These were deliberately designed to be compatible with Z80 and other systems that only have a 7 bit (128 cycle) refresh system.
OKI M3764A-15 DRAM chips fit the above requirements (128 cycle, 7 bit refresh and an access time of 150ns).
TI TMS4164-15NL DRAM chips
do not fit the above requirements. The access time is okay, also 150ns. But they require a 256 cycle, 8 bit refresh.
The only way to know is if you happen to find a copy of a chart on the internet that lists these details. Or by very carefully reading the manufacturer’s datasheet or data book.
Or if you buy from a reputable seller, but make sure you tell them you need the type with the 128 cycle refresh.
On trading sites, be careful. As it’s not uncommon for descriptions to be copy and pasted, and hence be misleading…
Here is one trusted seller
Mark
Standby alert 