On Wed, 13 Oct 1999 22:19:31 -0400 "Sean H. Breheny" writes: >Yes,it is possible. The best way is to use an external oscillator with >sufficient drive and then route the output to all of the OSCIN pins on >the >PICs (I forget which pin this is,but it's in the datasheet). I think >you >also want to put the PIC in HS mode (again, going from memory, it >might be >XT). > >A thought occured to me about the synchronization: Commands like BSF >and >BCF should always output to the port pins on the same cycle,right(I >think >its Q4)? Why not make a piece of hardware which sends the clock to >several >PICs simultaneously. However, to sync them, it runs the clock very >slow and >withholds the clock from all but one PIC at a time. Each PIC is >programmed >with several BSF and BCF commands. The clock hardware would feed the >clock >to each PIC individually until it saw a rising edge (BSF) on an output >pin. >It would then go to the next PIC, do the same. Then, you would have >all the >PICs at the same Q phase,and you could simultaneously feed the normal >fast >clock,and the special clock gen could be turned off. The special clock >circuit could even be a PIC itself. > This reminds me of the old weather map fax machines I used to work on for the FAA. They used soggy paper and passed current thru the paper to turn a pixel brown. The paper was pulled over a drum that rotated with a helix contact on it. There was also a contact band above the paper. As the drum rotated, we got a horizontal scan across the page. The motion of the paper gave the vertical scan. At the beginning of each map was a black bar with a white horizontal sync pulse. On detecting this, the oscillator that drove the synchronous motor driving the helix drum changed from 60 Hz to 59 Hz or so. The motor would continue to run at this speed until a magnetic reed switch on the side of the drum closed during the received sync pulse, indicating the sync pulse was now at the edge of the picture. The motor then changed back to 60 Hz. At the top of each map was this black bar with a white diagonal stripe going down and to the left until it hit the left end of the paper. The oscillator for the motor was a crystal oscillator with a digital divider chain. As I recall, they changed the digitial division ratio to slow the motor down. The oscillator/divider chain then drove a big transistorized power amp that drove the motor. The only problems we EVER had with the machine were due to the power amp blowing up. Harold Harold Hallikainen harold@hallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.