MCP2155 Performance

Hello!

I'm developing a board based on the MCP2155 to transfer data via IrCOMM between a PDA (Compaq Ipaq - Pocket PC) and a device connected to the board. I've already set it up to work, but i can only achieve a transfer rate of about 12000bps. The MCP2155 datasheet asserts it can achieve "typical" rates of up to 38000-50000bps. I've repeated the test with a WinXP-laptop instead of the PDA but the results were the same.

I've verified that the actual infrared bitrate (on the air link) is

115200 and i transfer data also at 115200 on each side. Since I was quite disappointed with the effective bitrate, I connected an oscilloscope to the MCP2155 and i observed the following repetitive pattern during the transmision of a file from the MCP side to the PDA:

(approximate time measurements)

1) The primary (PDA) transmits for about 12'5 msec (144 bytes @ 115kbps) 2) Less than 1 msec later, the PDA activates its CTS output. Now is when i feed the MCP with the file data, until CTS deactivates. CTS stays active for about 5 msecs (~64 bytes @ 115kbps) as i expected.

3) Now comes the big problem! ~25 MSECS of innactivity LATER the MCP starts to transmit, for about 7 msec (~80bytes @ 115kbps).

4) After a brief turnaround of 2 msec, the PDA transmits again and it starts over from 1)

Summarizing: the MCP has transmitted effective data for 7msec of a period of 50msec, so it is working at 14% of the IR bitrate, which renders the ~12000bps bitrate i get. The delay in 3) (which i don't understand what is due to) and the long transmission time of the PDA in 1) (which surely has to do with the Irda Stack in the PDA) spoil the effective bitrate.

Has anybody an explanation for that strange delay in 3)? or simply, Has anybody got higher bitrates between the MCP and a commercial Irda Stack?

Many thanks in advance!! Victor

Reply to
Victor
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Caveat: I have no experience at the low level of IrDA.

Given that caveat, a suggestion: Test with the tx and rx at least 30cm apart. I've had unusual problems with IR transfers when the separation was too low.

Reply to
Lewin A.R.W. Edwards

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