Path: utzoo!utgpu!watmath!isishq!f171.n221.z1.FIDONET.ORG!izot From: izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh) Newsgroups: comp.sys.cbm Subject: Re: C128,C128D, and C128C??? Questions Message-ID: <1896.24298458@isishq.FIDONET.ORG> Date: 23 Mar 89 13:21:03 GMT Sender: ufgate@isishq.FIDONET.ORG (newsout1.25) Organization: FidoNet node 1:221/171 - Izot's Swamp, Kitchener ON Lines: 77 > From: elg@killer.Dallas.TX.US (Eric Green) > Message-ID: <7606@killer.Dallas.TX.US> > I don't have a Z-80 manual lying around (I'm not ancient enough ;-), > but I also suspect that a 4mhz Z-80 takes less time for internal > processing than a 1mhz 6502. e.g. moving B to A may require less time > than moving .X to .A on 6502. Argh. My Z80 manual is in Toronto and I'm in Kitchener. However, I do have a comparison chart handy that gives execution times for an 8-bit immediate add to accumulator: Processor Op Code Cycles Speed Time ---------- ----------- ------- ------- ----- 6502 ADC # 2 2 MHz 1 us 6800 ADCA # 2 2 MHz 1 us 8085a ACI # 7 5 MHz 1.4 us Z80A ADC A,# 7 4 MHz 1.75 us From this table, I can conclude that you're probably better off using the 128's 2 MHz 6502 than its Z80. I should also mention the 6809 here. It offers 16-bit registers (accumulator, two index registers, user & system stack pointers), a direct page register (to move zero page around, as is possible with the 128's MMU), and an 8 bit by 8 bit unsigned multiply that takes 11 clock cycles! I've heard that OS/9 is a Unix-style operating system for the 6809... if so, I'm not surprised, considering that the 6809 deserves the title "16-bit" almost as much as the 8088 does, and its design is much more efficient. > There seems to have been a design decision, somewhere in the software > cycle, to switch into 6502 mode and use the Kernal for all I/O. Makes the BIOS ROM shorter and saves time re-inventing the wheel. > if the Z-80 > was handling all its own screen and modem i/o, that'd solve the two > biggest problems of the 128's CP/M mode. Miklos Garamzeghy has published a C128 CP/M disk I/O toolkit. Admittedly, RS-232 would be faster if it didn't have to "spawn" a processor switch at every interrupt. Fred: would VDC DMA work with the Z80 controlling the bus? > (and, BTW, there is a > program available to turn off the 40 column screen -- it does speed up > compute-bound programs, but does little to speed up slow I/O > operations). THAT sounds interesting! > I solved the screen i/o problem by buying an Amiga ;-). Problem NOT solved. Have you ever tried scrolling a 16-colour screen at 9600 bps? EVen an 8-colour? The time lag between the scrolling of bitplanes smears the characters badly (they're often unreadable) and, even with Agnus doing the hard work, I have yet to see an Amiga terminal that won't eventually lose characters when scrolling at 9600 bps (our C128 terminal program doesn't... does that indicate that a 2 MHz 6502 with DMA video memory makes a faster terminal than an 8 MHz 68000 with custom graphics coprocessor?) ============================================================================ Usenet: watmath!isishq!izot | 66 Mooregate Crescent Internet: Geoffrey.Welsh@f171.n221.z1.fidonet.org | Suite 602 FidoNet: Geoffrey Welsh on 1:221/171 | Kitchener, Ontario PunterNet: 7/GEOFFREY WELSH | N2M 5E6 CANADA BBS: (519) 742-8939 24h/7d 9600 USRobotics HST | (519) 741-9553 ============================================================================ | "I don't need a disclaimer. No one pays any attention to what I say." | ============================================================================ -- Geoffrey Welsh - via FidoNet node 1:221/162 UUCP: ...!watmath!isishq!171!izot Internet: izot@f171.n221.z1.FIDONET.ORG