C51: Using Only One Registerbank

Information in this article applies to:

• C51

QUESTION

What does the ONEREGBANK compiler directive do?

ANSWER

When the C51 compiler generates code for an interrupt function that is declared without a USING directive, register bank 0 is selected by default. For example:

void ISR (void) interrupt 1
{
func (counter++);
}

generates the following interrupt entry code:

             ; FUNCTION isr1 (BEGIN)
0000 C0E0              PUSH    ACC
0002 C0D0              PUSH    PSW
0004 75D000            MOV     PSW,#00H

Setting the PSW is necessary when you use both high-priority interrupts and low-priority interrupts. If a high-priority interrupt is declared without a using directive, the compiler assumes you want to use registerbank 0. This is required when interrupting low-priority interrupts that HAVE specified a registerbank (with the using directive). By default, the C51 compiler uses this technique to ensure that high-priority interrupts that do not specify a registerbank with the using attribute can interrupt lower priority interrupts that use a different registerbank.

If you only use one registerbank in your program, you can use the ONEREGBANK directive to tell the compiler to avoid selecting registerbank 0 in interrupts that don't specify the using directive.

SEE ALSO

• C51: Version 6 Release Notes

Last Reviewed: Thursday, February 25, 2021