"Christian Groessler" > > The 4-position DIP switch is a giveaway--it's a Microsoft SoftCard > > clone. > What are the dip swiches used for? According to my softcard schematic: s1 address offset disable s2 Z80 DMA s3 Z80 NMI s4 Z80 IRQ All are normally off. s1 remaps Apple's bottom 4k memory to upper 4k space and i/o right below it. This gives maximum contiguous RAM for CP/M and avoids conflict with Apple text video memory and 6502 zero page, stack and other system memory areas. s3+s4 send bus interrupts to the Z80 (if you we're going to have the softcard to interrupt handling--unlikely) s2 controls DMA. This is used by a few hard disk controllers, but I don't think this is ever used when the Z80 is active. Theoretically, if you didn't care about the 6502 (which is normally used to handle all i/o), you could rewrite the BIOS to have the Z80 do all i/o (which is normally handled by calls to 6502 routines), you could gain an extra 4k of ram. You'd have to use an external terminal, because Apple's video memory would be over-written by CP/M's transient program area. I doubt anybody has ever done this. The Softcard was toggled on or off by a read of its slot memory (not i/o) space--i.e.$C4xx for slot 4. The Softcard was a clever and efficien design to have the Apple double as a CP/M computer. It was one of Microsoft's few early ventures into hardware design. But it served to expand their market for their CP/M based products (mainly computer languages at that time). In article , Christian Groessler wrote: > mjmahon@aol.com (Michael J. Mahon) writes: > >> Christian Groessler wrote: >> >>> Formatting with 2.2 does work, thanks. >>> What card I have? I don't know :-) I got it from ebay and it has 4 dip >>> switches and no hint who the manufacturer is. >>> But it works so I don't care :-) >> >> The 4-position DIP switch is a giveaway--it's a Microsoft SoftCard >> clone. That's handy, since most Apple CP/M software was intended >> to be run with the SoftCard. > > What are the dip swiches used for? They're used to control various pieces of hardware behaviour for the SoftCard. With one of them, you can for instance turn off the hardware translation of Z80 addresses to 6502 addresses; with another one you can make the Z80 execute at full speed (4 MHz) instead of running two cycles then idling two cycles (allowing the 6502 CPU to refresh its internal registers). But if you do any of this, Softcard CP/M won't work... :-) For use with Apple Softcard CP/M, all four switches should be in the OFF position. The only reason to want to put them in some other position would be if you didn't run SoftCard CP/M but some of your own custom Z80 code (if you want to do this, the Z80 Cross Assembler version of the S-C Assembler could be useful -- it's available for download at my Apple II page at tiscali.se -- see my .sig for the full URL). However I know of no software which needs these switches to be set in any other position than all four being OFF. If there's interest, I can dig up information about what these switches actually control. -- ---------------------------------------------------------------- Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF) Grev Turegatan 40, S-114 38 Stockholm, SWEDEN e-mail: pausch at saaf dot se WWW: http://hem.passagen.se/pausch/index.html http://home.tiscali.se/~pausch/