How to modulate Transceiver module for use with ATmega164PA

Question

I am using a transceiver TFDU4101-TR3 to communicate with another device which has exactly the same transceiver. I bought this thinking I can communicate with the transceiver using my microcontroller ATmega164PA running at 8 MHz at 3.3V. Turns out I cannot use serial without the endec which I cannot buy because of budget constraints.

So I was looking to use the RxD and TxD pins on the transceiver to somehow modulate the signal. I made my PCB ages ago and the transceiver connects to the microcontroller through RX and TX lines. Can I still modulate the signal using RX and TX pins on the micro as GPIOs?

I was looking into pulse width modulation but for that do I need to connect the transceiver pins to OCxA and OCxB pins on the micro? Can I still make do with RX and TX pins on the micro used as GPIOs and somehow use that in conjunction with PWM?

Answer 1

IRDA 'modulates' RS232 by converting it to/from RZI (Return to Zero Inverted). An ATmega164 running at 8MHz should be fast enough to 'bit-bang' this format on standard GPIO pins, but timing is critical so it won't be able to do much else at the same time.

You could use AVR304 (http://www.atmel.com/webdoc/atmel.docs/atmel.docs.33085.18343.html) as a starting point for your own code. Modify the Transmit code to generates a short pulse for each '0' bit, and during Receive if a pulse is detected then the bit is a '0' ('1' bits are represented by no pulse occurring during the send or receive bit time).

It might be possible to use hardware PWM for generating the transmit pulses, but I would try software timing first because it's easier (you can try other techniques once you get it working!).