Due to timing requirements the standard z80 chip in the c128 is rated for 4MHz, and it gets clock pulses at that frequency but the clock will “sleep” from time to time to fit the bus structure of the 8502. Thus the effective clock is only 2 MHz normally, even if the chip is rated for 4 MHz.
OMG this video was so exciting! 8 MHz Z80 on the C128?? AMAZING! Hey did you ever figure out what the Z80 you used in this video was rated for? Also: your virtual drive: Does it use the burst mode that the C1571 and C1581 uses?
Pretty cool. I have to dig into what all the other mods you have are but getting the Z80 up to 4 MHz is definitely something I'd like to do with my C128. But it's also a wedge so we'll see if I can get it to fit.
Form the wiki sheet the C128 has an Z80A or Z80B are 4MHz CPUs but they run at only 2MHz on the C128. Will you get an 8MHz Z80? If it will work at 8MHz that will 4X faster than the 2MHz it runs at now.
8MHz operation should in theory be possible in the C128's 2MHz mode... The VIC-II doesn't double the clock speed of the Z80 like it doubles the clock speed of the 8502 in 2MHz mode, however, there is no reason why this is not possible. Therefore it should be possible to get 8MHz operation, but the challenge will be to replicate the cycle stretching that the VIC-II does during memory refresh and I/O access.
Those drives were so sloooow. I remember playing zork on a friend's c64 . He typed in a command, 5 minutes of drive whirring around to finally spit out "you have died"
So instead of really slow to slow? :) I'm pretty sure I said this before some place. When I saw the c128 could run cpm. I was like heck yea. Thinking of Kaypro. Then I found out how slow it was.
If you use this mod in combination with the optimized versions of CP/M that have been release over the years, the C128 should become a fine CP/M machine. At 2MHz the C128 was underpowered, but at 4MHz, it compute power it pretty competitive to other CP/M machines.
