29

06/19/2000

GL600USB/GL600USB-A/GL600USB-B

Revision 1.3

5.6

Timer Interrupt

Because CPU may enter timer interrupt routine at any time, the timer interrupt routine should

backup all special registers at its entry point and restore them before return.

(Address 0x004)

TIMER_ENTRY:

MOV

A_TEMP, A

SWAPR

A, STATUS

BCR

STATUS, BS

MOV

S_TEMP, A

MOV

A, INDAR

MOV

I_TEMP, A

;

; Execute interrupt service routine

;

MOV

A, I_TEMP

MOV

INDAR, A

SWAPR

A, S_TEMP

MOV

STATUS, A

SWAPR

A_TEMP

SWAPR

A, A_TEMP

BCR

INTEN, TMROF

RETI

5.7

Conditional Branch

Example: Conditional branch can be according to value of Accumulator. Firmware can use this

method to return value for lookahead table. Because Accumulator is only 8 bits wide, the higher 3

bits of Program Counter should be load into PCHBUF before the conditional branch executed.

(Address 0x540)

LOOKAHEAD:

MOVIA

0x05

MOV

PCHBUF, A

MOVIA

LOOKAHEAD_VAL

ADDAR

PCL, A

RETIA

0

; Acc = 0

RETIA

1

; Acc = 1

RETIA

2

; Acc = 2

.

.

.

.

.

.

5.8

Change Register Bank

Usually keeps BS = 0. If firmware want to access register address 0x80 to 0x8F, set BS = 1. After

process register address 0x80 to 0x8F complete, clear BS = 0 to address 0x00 to 0x7F.

BSR

STATUS, BS

MOV

PORT1CON, A

BCR

STATUS, BS