Harold,

>         I don't think you can hit 250 kbps with 20 MHz.  I use 16 MHz.

    According to page 109 of the PIC16F87X literature (DS30292A), with
FOSC=20MHz, BRGH=1 and SPBRG=10, the USART works at 250Kbaud with 0%Error.

>         Since each byte is 11 bits (start, 8 data, 2 stop), and takes
> 4uS, I'd have the timer generate an interrupt every 44 to 50uS.  I then
> use that to either dump a byte into the transmit register or generate a
> break.  Since the USART does not have a break command, I used another I/O
> pin for that.  The USART output pin goes through a resistor to the 488
> driver.  The input of the 488 driver ALSO connects to another I/O pin
> that is normally in the input mode with the output bit set low.  When I
> want to do a break, I change the pin to output mode, passing through the
> low in the output latch, shorting the resistor isolated data to ground...
> instant break!  At the next timer interrupt, the pin is changed back to
> input.  Another interrupt later, the USART is loaded with the next byte
> (the start code).  The "one interrupt" between end of break and sending
> the next character insures there is adequate mark after break (MAB).
> Here, it's a litte over one byte's time (44 uS).

    I thought that stoping telling the USART to output a byte would maintain
it in idle mode, so, with it's output HI (the same as a break). Isn't it?

>         Is it a multiplexed display?  Can the display routine be called
> by the same timer interrupt?

    Yes, I'm multiplexing it, and it could probably be called by the same
timer interrupt. I'll try both it ways.

>         Couple reasons...  A tremendous amount was invested in the
> software that runs on the PC.  This was written before I got here, but it
> came with the aquisition of another company plus lots of maintenance, and
> finally my interface code to the StarPort (which is a very small part of
> it).  We're SLOWLY moving it over to Windoze, but I keep getting
> sidetracked onto other projects.  Reason #2...  It's about where the
> competition is...

    Ok, I'll dive deeper at DOVE site to see the cool things you are doing.

    Best regards.

    Brusque
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