Sinclair ZX80 / ZX81 / Z88 Forums

I was able to demystify the WRX miracle. It had been an layer 8 error(located between my ears). All of the programs I used for testing WRX invaders.p pacman,p Against_The_Elements (Paul Farrow 2016) [V1-01].p were pseudo HRG programs in actual fact. So I searched around for real WRX programs and fou...

From the beginning Minstrel is able to run: - Low res graphic(e.g. 3D Monster Maze, 3DMonsterMaze.p) - Pseudo hi res graphic(e.g. Manic Miner, manic.p) - WRX hi res graphic(e.g. Space Invaders , invaders.p) but not - UDG hi res graphic(e.g. Breakout, breakout.p) - CHR$128 hi res graphic(e.g. Panic H...

The chips arrived and I implemented the circuit on my Minstrel board. Works fine, no unexpected writes on shutdown. Only issue I found is when Battery is low or absent, the second access to RAM is ignored(described in the datasheet), so operating system does not start at power up but after additiona...

Looks interesting. A couple of questions. What extra software can you now run with the 56K RAM that couldn't run before, and are there any programs which did run with 16/32K but will not work with the extra RAM? I have not found much software which needs more that the standard 16K, so trying to jud...

ZXpand+ had been available at 20th of January for 2h and 28min.

https://www.sellmyretro.com/offer/detai ... ing.-40565

The way to 56k: As already mentioned I replaced the 32k x 8 SRAM(IC2) by an 128k x 8 SRAM. As this doesn't fit into a 28 pin socket, I took a 32 pin socket and cut of the legs 1,2,31 and 32. Pin 1 is Not Connected at the 128k chip, pin 2 is A16. As I decided to use up to 64k I connected both of the...

There is a ready made solution for battery backup for SRAM: Maxim DS1210 https://datasheets.maximintegrated.com/en/ds/DS1210.pdf Chip is also available from Dallas Semiconductror This chip support 2 batteries, ensure that SRAM is disabled in case of power down and is able to detect brown out at 4.75...

The way to 56k: As already mentioned I replaced the 32k x 8 SRAM(IC2) by an 128k x 8 SRAM. As this doesn't fit into a 28 pin socket, I took a 32 pin socket and cut of the legs 1,2,31 and 32. Pin 1 is Not Connected at the 128k chip, pin 2 is A16. As I decided to use up to 64k I connected both of them...

So I come back to "diode and pull up resistor" solution: Do you think, separating 74HC257(IC24 PIN 4,7,9,12 and IC25 PIN 4) by a set of diodes from data bus, enabling the IC to pull data lines to low and pull the data lines to high by a set of resistors may work with ZX-Key expansion card? This may ...

Ok. that make things difficult. Splitting IC25 into one that is handling D5, NTSC/PAL and EAR(not disabled) and another one that is handing /COL4(disabled when no key is pressed) may fix that but we have added 3 chips for that feature now. Reason why I'd like to solve that is that I am planning to h...