palmer@nntp-server.caltech.edu (David Palmer) (02/02/91)
I'd like to build some hardware that stuffs data as fast as possible into the serial port of the Mac. I know the tricks used in MacRecorder: 1) External clock, with a clock rate equal to the bit rate 2) turn off interrupts 3) access the serial port hardware directly 4) tight software loop Given that, how fast can you run the serial ports on the various models of Mac? Is there any way to avoid breaking the Apple rules to do this sort of thing? Any other tricks? (I am not ready to go SCSI). Thanks in advance. -- David Palmer palmer@gap.cco.caltech.edu ...rutgers!cit-vax!gap.cco.caltech.edu!palmer "Operator, get me the number for 911" --Homer Simpson
beckmann@s28.csrd.uiuc.edu (Carl J. Beckmann) (02/05/91)
palmer@nntp-server.caltech.edu (David Palmer) writes: >I'd like to build some hardware that stuffs data as fast as possible >into the serial port of the Mac. >I know the tricks used in MacRecorder: > 1) External clock, with a clock rate equal to the bit rate > 2) turn off interrupts > 3) access the serial port hardware directly > 4) tight software loop >Given that, how fast can you run the serial ports on the various >models of Mac? The Z8530 serial chip ought to be able to go pretty fast in synchronous mode. Don't quote me because I don't have my Z8530 manual handy, but it'll probably do at least 1 M bit/s. And if you access the chip directly with a very tight loop, the 68000 (020, etc.) ought to have no trouble keeping up. The REAL bottleneck is probably the serial drivers and receivers. I don't know what their limits are, but "Inside MacIntosh" (volume II?) has a diagram of the serial ports showing RC filtering on those ports. You could take the RC time constant, multiply by 10, and invert to get a ballpark estimate. By the way, do you have any technical info on MacRecorder (i.e. how to write your own software to access it directly)? Thanks in advance. -Carl beckmann@csrd.uiuc.edu
awessels@ccwf.cc.utexas.edu (Allen Wessels) (02/06/91)
In article <1991Feb2.062244.3235@nntp-server.caltech.edu> palmer@nntp-server.caltech.edu (David Palmer) writes: >Given that, how fast can you run the serial ports on the various >models of Mac? The Mac Plus specs give .92 megabits per second if clocked externally.