piclist 1999\10\27\194548a >
Thread: DMX Sender (have I use one or two PICs?)
www.piclist.com/techref/displays.htm?key=dmx
picon face BY : Harold M Hallikainen email (remove spam text)



On Wed, 27 Oct 1999 20:24:51 -0200 Edson Brusque <brusqueKILLspamspamspamBeGoneFLYNET.COM.BR>
writes:
>Harold,
>
>
>    I'll try to redesign the code using the USART of the PIC16F877.
>I'll run the PIC at 20MHz, so it'll give me no error rate.

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

>I'm thinking of using a TIMMER interrupt running once each 240
instructions (12 bits), and
>each time it is invoked, I'll give instructions to the USART to send one
byte.

       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).

>The LED display will be running with another TIMMER interrupt. The
keypad will
>be handled with the RBINT interrupt. Hope this will work...

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

>
>    Best regards and thanks for all your help,
>

       You're welcome!  I get a lot of good ideas from the list, so I'll
share a opinions on stuff...


>    Brusque
>
>P.S.: I've took a rapid look at DOVE SYSTEMS site. Why is the StarPort
>so expensive?
>


       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...


Harold

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