Good Afternoon,

I'm trying to get the multiprocessor communication on the Atmel T89C51AC2 working.

I am using UART Mode 1 as per the manual, 1 start, 8 bits, 1 stop.

My master controller is currently setup with this code:

//Multiprocessor Communication Registers
unsigned char *SADDR;
unsigned char *SADEN;

//Setup Multiprocessor communication
SADDR = (unsigned char *)0xA9;
SADEN = (unsigned char *)0xB9;

*SADDR = 0x3e;
*SADEN = 0xff;

My slave has the same code except SADDR is 0xff. When my master uP sends data, the slave still continues to receive it. Even though my understanding of this is that if the set bits of

(master)(SADDR | SADEN) != (slave)(SADDR | SADEN)

then the slave will not set the RI bit.

Is there something I am missing here?

Thanks,
Roque