Setting S0RIR

Have you checked the serial line with an oscilloscope?
Do you use the Debugger (which also uses S0)?

Have you checked the serial line with an oscilloscope?
Do you use the Debugger (which also uses S0)?

I have found a solution to my problem. The receive code needs to be as follows for it to work correctly.

while( !S0RIR & !S0EIR ) ;
rx_char = ( uint8_t ) S0RBUF ;
S0RIR = 0 ;
S0EIR = 0 ;

I thought that the S0EIR flag was set simultaneously with the S0RIR flag from my reading of the manual.

I thought so too. According to the manual, in your piece of code

while( !S0RIR & !S0EIR ) ;

while( !S0RIR ) ;

while( !S0RIR && !S0EIR ) ;

while( !S0RIR & !S0EIR ) ;

while( !S0RIR & !S0EIR ) ;

Hi Again

This code works at 9600 baud but seems to have problems at higher rates and is contrary to the manual.

uint8_t GetByte( void )
{
	uint8_t rx_char ;

	while( !S0EIR && !S0RIR ) ;

	rx_char = ( uint8_t ) S0RBUF ;
        S0RIR = 0 ;
	S0EIR = 0 ;

	return rx_char ;
}

uint8_t GetByte( void )
{
	uint8_t rx_char ;

	while( !S0RIR ) ;

	rx_char = ( uint8_t ) S0RBUF ;
        S0RIR = 0 ;

	return rx_char ;
}

Well, without an in-circuit debugger you can never be sure what's going on. Besides, hardware problems is always a possibility (floating NMI pin, for example.)
Set up debugging with Monitor166. Even if there is no external RAM in your target hardware, you should be able to debug small pieces of code with 6Kbyte of XRAM.

Good luck!
- mike

Servicing my non-running watchdog timer means that the code now works fine.

    while( !S0RIR )
    {
        _srvwdt_() ;
    }

    rx_char = ( uint8_t ) S0RBUF ;
    S0RIR = 0 ;

The watchdog timer is running unless you stop it before an EINIT or SRVWDT instruction.

Sauli