Arg! Help! What happened???!! I went away for the weekend, and I just came back to several thousand mail messages.... :)
Err.. now, what was said in most of them??? Yeah, the Z8108 needs a 12Mhz clock input, which is divided internally by two for its base clocking rate (6Mhz).. which will also be the rate of the bus. Now, you can set a register on reset by holding the WAIT line and sending a signal down the data bus to it, to set an internal register which controls the clock multiplier, so it can run at 1, 2 or 4 times of the base rate internally.. god knows how I'm going to sort THAT one.. :) Right, the Z8108 uses a super-set of the Z80 instruction set, at a binary level, including all the undocumented Z80 op-codes which are now finally documented.. there are hundreds of extra commands, most of them true 16 bit commands, since the Z8108 is a 16 bit chip. These include 8 and 16 bit multiply and divide commands. A good one is that the refreshes are now programmable, and no longer handled by the R register, which you can use as you like.. Internal registers also control things like wait states, so I'm wondering.. are some of us thinking of the same chip but with a different designation?.. :) It SHOULD run a fair bit faster, because among other things it's got an internal memory cache that can either be used as memory or a Most Recently Used Instructions data file.. all software transparent, of course.. :) However, if this doesn't seem enough, the Z8108 has got a few spare address lines, which allow it to access 512K of memory. It's got internal page registers, and you can map any 4K section to any area of memory. What I was thinking of doing was using the base 64K as the SAMs paged memory, controlled by the ASIC, and bunging on some extra memory, which would be mapped above this. Admittedely, this won't run any faster, but it's nice to know that you've got some extra memory.. :) Of course, I could use a Z8116 which addresses 16Meg, and has got 4 programmable DMA's.... Yup. Those that DO know the SAM inside out end up thinking.. "Oh. Is that it?". Of course, given the money, a completely redesigned computer wouldn't be the SAM, but you could keep it SAM compatible without merely running an emulation.. look at the SAM itself.. it doesn't so much emulate a spectrum as become one..... DMZ -- Yet another witty yet deeply meaningful phrase at the end of === the name that should make you all sick. Come on... it was only a FEW lines... :)
