16K RAM pack

[1024MAK]

… in the same way as an issue 2, which can be expanded to 64K using 4164 chips by piggybacking some extra array manipulation chips on the additional PCB.

Ahh, but which class of 4164 DRAM chips? Those with 7 bit / 128 cycle refresh, or those with 8 bit / 256 cycle refresh? Or those with /CAS before /RAS refresh that means that they do their own internal refresh (meaning no external refresh counters are needed)?

Questions, questions, questions…

Mark

[sP1d3r]

Ahh, but which class of 4164 DRAM chips? Those with 7 bit / 128 cycle refresh, or those with 8 bit / 256 cycle refresh? Or those with /CAS before /RAS refresh that means that they do their own internal refresh (meaning no external refresh counters are needed)?

Questions, questions, questions…

Mark

Here's the link to the article, Mark:

https://www.timexsinclair.com/article/u ... am-pack-2/

I haven't yet got as far as the specific DRAM details.

[sP1d3r]

Questions, questions, questions…

The article in the magazine referred to in the link is p16-18 and makes no specific mention about which type of 4164 DRAM to use.
In the article the author, Tim Stoddard says that he also designed a 64K ram pack using newer 4164 DRAMs and that he was thinking of submitting his design to the Time Designs magazine.

The preceding article in the previous issue of the magazine, p35-36 of Time Designs v2 n6 may give some more insight into the logic, from what I can so far understand the author makes use of RAS only refresh to refresh an entire row of memory locations in the 4 x 16K blocks, requiring 128 refreshes for the entire 64K memory chip.

[sP1d3r]

Here's some pics of the 1016 16K RAM pack, it's a weighty little number and I can only imagine that it's more prone to wobble than other 16K ram packs I've seen.

Timex Sinclair 1016 16K RAM pack 2 internal PCBs

Solder side

[1024MAK]

…from what I can so far understand the author makes use of RAS only refresh to refresh an entire row of memory locations in the 4 x 16K blocks, requiring 128 refreshes for the entire 64K memory chip.

Normal refresh is indeed “RAS only”. From the above (not looked at the article), it sounds like he used 7 bit / 128 cycle refresh DRAM chips.

These were deliberately designed to be compatible with systems that use 7 bit / 128 cycle refresh like Z80 systems.

Mark

[sP1d3r]

Normal refresh is indeed “RAS only”. From the above (not looked at the article), it sounds like he used 7 bit / 128 cycle refresh DRAM chips.

These were deliberately designed to be compatible with systems that use 7 bit / 128 cycle refresh like Z80 systems.

I wonder if newer 4164 DRAM chips are backwards compatible with the older types?

[1024MAK]

The ones that have 7 bit / 128 cycle refresh, yes.

The others, partly. As in they support/RAS only refresh even if they have more sophisticated refresh modes.

Mark

[1024MAK]

The point I’m trying to make, is that a 8 bit / 256 cycle refresh DRAM using /RAS only refresh in a system that only provides a 7 bit / 128 cycle refresh will suffer from memory fade (for some of the memory) if the processor (or video system or both) does not access the addresses that use address bit A7 often enough (which bit depends on what state A7 is when the refresh address is presented to the DRAM). Because the 7 bit / 128 cycle refresh system does not provide a counter for address bit A7.

Mark

[sP1d3r]

Thanks Mark, I think I'll check some datasheets before I buy any 4164 chips because I wouldn't mind a 64K RAM pack, but not one with data retention problems.

[sP1d3r]

I've found another Timex Sinclair 1016 RAM pack, it's in good condition but it seems to have had a problem with one of the 74LS157 chips necessitating a replacement.
The problem seems to have caused the DC-DC converter coil to overheat and the enamel on the inner windings has darkened.

Timex Sinclair 1016 component side

Solder side

This RAM pack might make a suitable candidate for a 64K expansion, which makes the DC-DC converter redundant because 4164 DRAMs use 5V so I'd save myself the bother of rewinding the coil.
Rewinding a coil that's overheated is a good idea but care must be taken.
I've done it a few times with Spectrum coils, you desolder the wires and replace with an equal length of the same gauge of enamelled copper wire taking care to avoid scraping any enamel off the wire.

I've not yet tested the RAM pack to see if it works.