I have an evaluation board with a target and a control FPGA. The control FPGA is connected to the target FPGA over 32-bit local bus and can write the data to a host PC over a RS232 interface. Both FPGAs are internally clocked with 24MHz. So I have to implement on the control FPGA a transmitter that gathers the 32 bits and sends them in 8 bit chunks to the host PC. I wonder if somebody has some helpful ressources how to implement such an simple interface. Also I have to implement a suitable divisor for the baudgenerator to generate 115200 Hz from 24MHz.
Would be thankful for helpful comments and ressources ;)
Dan!
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Rob Gaddi
There are a couple of UART cores available on OpenCores that you can take a look through. Other than that, I seem to recall that Ken Chapman's UART implementation that comes packaged with the PicoBlaze core works pretty nicely.
-- Rob Gaddi, Highland Technology Email address is currently out of order
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Jonathan Bromley
I'd recommend you do NOT try to send a 32-bit word as 4 bytes over a UART. Instead, find some way to represent the 32-bit word using plain text (printable ASCII characters in the range 0x21-0x7E). Plain ASCII hex is an obvious choice, but rather extravagant (at least 8 characters per
32 bits); if throughput on your serial port is not a big problem, plain ASCII hex is good because it's so easy to generate and debug. If you need better throughput, you can use btoa or uuencode tricks to put the 32 bits into 5 or 6 plain-text characters. Think, too, about how you can reliably indicate the boundaries of your "here's a word" messages. A newline character on the end of your 8-character hex word is an easy and reasonable choice, and again is very convenient for debug.
24MHz/13 is almost exactly 16x115200Hz. Plenty close enough for a UART clock, anyway.
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Jürgen Böhm
A sample implementation for a serial receiver/transmitter with explanations about the used methods can be found at the very recommendable site
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Jürgen
Jürgen Böhm www.aviduratas.de
"At a time when so many scholars in the world are calculating, is it not
desirable that some, who can, dream ?" R. Thom
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