Smart Radio RF620A and RF620RA modules

Hi,

I recently purchased the Smart Radio RF620A and RF620RA modules from RFsolutions (Datasheet: http://www.rfsolutions.co.uk/acatalog/DS620-3.pdf).

I have managed to get the modules to 'learn' each other (in telemetry mode only) i.e. the LED connected to the receiver flashes 5 times. I got this working with 'Telemetry Mode'.

I then reset the transmitter module by holding the button down for 10 seconds as the datasheet says, the module flashed quickly indicating that it had been correctly reset.

I then connected the 10k Mode resistor on the transmitter to Vcc (5 volts) and tried to learn the modules together only this time in 'serial mode' however nothing happened (no lights flashed etc). I didn't change anything else on the circuit board and I double checked all the connections. I reverted back to telemetry mode and re learned the modules together so that still works correctly.

So basically I'm lost for ideas as to how to fix this...I am just getting erronious data from the receiver in both telemetory mode and serial when I hook an LCD up to the receiving PIC. As I said the circuitry all works if I bypass the RF circuit etc. Do I need to use some kind of level shifter (e.g. MAX 202 ?) with the PIC or something?

Note: I'm using a PIC16F84 sending the letter "R" serially to pin 1 of the transmitter as the datasheet suggests (this has all been tested independently of the RF link and works correctly etc).

Can anyone possible suggest what could be causing this problem?

Thanks,
Colin.