Code question

[danwinslow]

In this snippet of code ( the comments are mine ) :

 

SENDBYT TAX         ; save char to be sent

WPUT LDA IRQST         ; loop

AND #$10          ; until serial output data needed is true ( i.e., send completed )

BNE WPUT          ; end loop

LDA #$EF          ; 1110 1111

STA IRQEN         ; enable everything except serial output data needed (?)

LDA #$D0          ; 1101 0000

STA IRQEN         ; disable serial input data needed and timer interrupts

TXA               ; put send char back in A

STA SEROUT        ; put it (again) into xmit slot

LDX IRQST         ; load IRQ status

BPL ERR128        ; if N=0 goto ERR128 ( checking for break key? )

 

The BPL at the end looks like it is trying to detect a break key press..the preceding LDX from IRQ status would have bit 7 set if a break keypress had occured...which would cause the N flag to be *set*, not cleared...so the BPL seems like it is wrong. So what am I missing?

Edited December 13, 2005 by danwinslow

[DanBoris]

The bits in IRQST get set to 0 when the specific event occurs, not 1. So when the break key is pressed, bit 7 will be 0.

 

Dan

[danwinslow]

I was wondering about that. The docs I have say otherwise, but obviously they are not correct, or I didn't read them correctly. Thanks.

Edited December 13, 2005 by danwinslow