Richard, Erik,

Look at these code snippets and see what you gain by letting the SBUF access clear the flags.

uart_isr_explicit:
    push  ACC
    jnb   RI,transmit
receive:
    clr   RI           ;explicitly clear RI
    mov   a,SBUF
    ...                ;store it where you like it
transmit:
    jnb   TI,uart_isr_end
    clr   TI           ;explicitly clear TI
    ...                ;get next byte in a
    mov   SBUF,a
uart_isr_end:
    pop   ACC
    reti

uart_isr_jbc:
    push  ACC
    jbc   RI,receive   ;test and clear RI
    jbc   TI,transmit  ;test and clear TI
    sjmp  uart_isr_end
receive:
    mov   a,SBUF
    ...                ;store it where you like it
    jbc   TI,transmit  ;still have to do this
    sjmp  uart_isr_end
transmit:
    ...                ;get next byte in a
    mov   SBUF,a
uart_isr_end:
    pop   ACC
    reti

uart_isr_auto:
    push  ACC
    jnb   RI,transmit
receive:
    mov   a,SBUF       ;auto-clear RI
    ...                ;store it where you like it
transmit:
    jnb   TI,uart_isr_end
    ...                ;get next byte in a
    mov   SBUF,a       ;auto-clear TI
uart_isr_end:
    pop   ACC
    reti

The solution with jbc has a lot of jumps which is generally not a good thing if you want to pipe-line the core. It is also a few instructions longer. The explicit version is slightly bigger than the auto version but all things considered doesn't bring you that much. And if you think you can do multiple instrcutions in parallel it won't cost you anything.

Maarten