Another build
Posted: 20 Nov 2017 16:33
OK, it's not MTX related, or even Z80, but I've got another build running from some of the "extras" I received from Lez, via Dave.
Board 1: 6502 CPU, 32k ram, 8k rom, 6mhz clock, and 74 series logic to create a memory map
Board 2: 6847 VDG, 82C55 PPI, 8k ram, 74 series buffers to isolate the ram, 14.3mhz clock divided by 4 for the VDG (at the back)
Board 3: 6522 VIA, optional 6521 PIO and LCD diagnostic screen (in the middle)
It still needs some form of storage, but it's alive. The system I really wanted back in 1981 but couldn't afford, and had to settle for a ZX81 instead.
Theres no GAL or CPLD on the build, it's all done with logic chips, 74AHC for the most part, so the logic faster than the 74LS available as the time the original was designed. With modern static ram also havin a much better response time, I'm able to clock it 6x the speed of the original.
Screen output is currently mono, using the Y component only exactly as the original. Interestingly it's at NTSC frequencies, which no doubt cause a few issues back in the day.
Board 1: 6502 CPU, 32k ram, 8k rom, 6mhz clock, and 74 series logic to create a memory map
Board 2: 6847 VDG, 82C55 PPI, 8k ram, 74 series buffers to isolate the ram, 14.3mhz clock divided by 4 for the VDG (at the back)
Board 3: 6522 VIA, optional 6521 PIO and LCD diagnostic screen (in the middle)
It still needs some form of storage, but it's alive. The system I really wanted back in 1981 but couldn't afford, and had to settle for a ZX81 instead.
Theres no GAL or CPLD on the build, it's all done with logic chips, 74AHC for the most part, so the logic faster than the 74LS available as the time the original was designed. With modern static ram also havin a much better response time, I'm able to clock it 6x the speed of the original.
Screen output is currently mono, using the Y component only exactly as the original. Interestingly it's at NTSC frequencies, which no doubt cause a few issues back in the day.