ACE3NOKB V0 is a dud

I got the board altogether and there are some unfixable faults on it. There was 1 fixable which is the large kludge to the left of the board. That was because I misaligned the bus going into the IC so all that is to shift it 1 place left.

The more subtle problem is to do with the Chip Select on the video RAM. The system works by defaulting to having both ICs selected, this is done by pulling the CS pins low, this allows the Video circuitry access continually, it cuts down the time needed to access the chip but may put the power consumption up, which explains some hot running. The only times these pins are pulled high is when the CPU is accessing one of the video chips, when that happens the one not being accessed goes high. Anyway, I missed that trick and so the Video circuits could not access the RAM, other than that the worked a had a nice stable pattern.
So I've now fixed that in design V0.1 which will soon be off to China, I've also taken the opportunity to change the ROM layout that is using on his Minstrel 4th. This overlays the character RAM so that when the CPU writes to it it actually writes to the RAM but when it reads it reads from the ROM. This combined with the 3k of empty space between. 0x3000 & 0x3C000 gives 5k of space, which is 1k more than my last plan and also keeps base memory at the same location, meaning less rewriting of the ROM. I'm also considering using the Video RAM design similar to this as it only uses 1 Dual Ported RAM.
Meanwhile over on GitHub Ricardo Fernandes Lopes has started Jupiter-II.

 Which as you can see is very compact. The design of the timing cascade on Ricardo's machine is better than the original Ace using 2*74LS4040 rather the 3*74LS393 as well as using fewer chips it is also more elegant and easier to understand. Ricardo tells me he has built the first prototype and has tweaked his design and V 2 is at the PCB makers.

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