Wednesday, 26 April 2017

ZX Spectrum Project - Part 2

Today on the Spectrum I removed all of the old lower RAM chips and added sockets. I have spent the day trying to get a modern SRAM chip to take the place of all eight of  the DRAM chips, timings and support logic are proving to be a bit more of a challenge than I had anticipated. This has resulted in some extremely weird graphics on the screen. I have found that adding a little bit of logic can produce some unusual graphics.

Next I believe I am going to try using a micro controller to better manage the conversion as it appears that the signals have a bit more of a timing requirement rather than being purely logic driven. Think the ATTiny2313 for this task as it doesn't need too many pins and I don't think there will be too much processing power required.

I have also been working on the keyboard controller. This is purely theoretical at the moment as the Spectrum is doing the weird graphics stuff but this appears to be decoding the keyboard signals and mapping them to the correct responses.

I think tomorrow I will be attaching that to my other Spectrum to test it out.