home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!wupost!waikato.ac.nz!comp.vuw.ac.nz!actrix!David.Empson
- Newsgroups: comp.sys.apple2
- Subject: Re: Fast Zips
- Message-ID: <1992Jul29.114032.1215@actrix.gen.nz>
- From: David.Empson@bbs.actrix.gen.nz
- Date: Wed, 29 Jul 1992 11:40:32 GMT
- Sender: David.Empson@actrix.gen.nz (David Empson)
- References: <1992Jul27.210031.20138@micor.ocunix.on.ca> <1992Jul28.141402.6199@meaddata.com>
- Organization: Actrix Information Exchange
- Lines: 20
-
- In article <1992Jul28.141402.6199@meaddata.com> johnt@meaddata.com (John Townsend) writes:
- > My question is, how does one tell from software what
- > the maximum speed of the Zip GS is (e.g. on the Zip control panel)? Does it
- > do a timing loop or is there something on the board that indicates the speed
- > (which might have to be changed in addition to the components)?
-
- My guess is a timing loop. The percentage speed can be read from
- registers in the ASIC, but not what 100% corresponds to. The ASIC
- doesn't care, anyway - it just runs at 1/4 of the frequency of the
- crystal (assuming the processor and cache RAM are fast enough).
-
- The timing loop probably involves counting down a fixed number of
- clock cycles with interrupts disabled (e.g. DEX, BNE loop) and using
- the video counters or vertical blanking signal to get a CPU-independent
- reference.
- --
- David Empson
-
- Internet: David.Empson@bbs.actrix.gen.nz EMPSON_D@kosmos.wcc.govt.nz
- Snail mail: P.O. Box 27-103, Wellington, New Zealand
-