rmeier@SU-STAR.ARPA (R. MEIER) (03/28/85)
To:mailer!info-cpm@brl-tgr.arpa From:rmeier@star.arpa Ed, I have been using a Z80 card in my Apple ][+ for a year now without serious problems. Specifically, I use a Softcard from Microsoft. It came with CP/M 2.2 and runs a 2.1 MHz. It accomplishes this by using a nonsymmettric clock that is synchronized with the Apple's internal clock. The Apple's internal memory is used. I tried to rewire the card, so as to double its speed to 3.5 MHz, but this failed intermittently due to the fact that it exceeded the speed of the Apple's memory and I didn't think it worth the effort to add wait cycle logic. Their Softcard has worked reliably and timing experiments have shown that it works at a consistent 2 MHz, unlike some cards which use wait cycles to operate slower than the advertized clock speed. My only complaint against this card, is that the CP/M 2.2 that is supplied with it is rather inefficient in terms of memory and time. Memory cycle observations have shown that as many as 300 subroutine calls may be involved in a single bdos call. The operating system occupies 20K of memory. I have dreamed of writing my own unixlike operating system, but I don't expect that I will ever get the time. Bob ------