Hi,

I am working on a Real Time Clock interrupt service routine with UART communication for the P89LPC931 controller. The UART sends data out by TxD in this interrupt routine. The data I send out in this routine (eg. SBUF=65) is not the same as the data I receive on the serial port of the PC. The data that I receive on the PC is always the same with the transmission of a certain value from the controller. I checked the baudrate of the UART in the interrupt routine and it's the same as on the PC. I have tested the hardware and everything works fine in normal operation (outside this interrupt routine). The UART is running in mode 1, uses the Baud rate generator and has no double buffering. Interrupts for the UART are disabled. UART_TxD is configured as push-pull output. I tried all the register banks (0,1,2,3) of the interrupt routine, but without effect. If I understand correct, this only affects local registers (R0 up to R7) and not the global variables? Can you help me with this problem? Thanks in advance.

Kind regards,
Mark