NEC PD750008 User Manual

3 6

µPD750008 USER'S MANUAL

(2) When used as an 8-bit register

When the general register area is used on an 8-bit basis, the register pairs in the register bank specified

by RBE·RBS can be specified as XA, BC, DE, and HL as shown in Figure 3-6, and the register pairs in

the register bank that has the inverted value of bit 0 of the register bank (RB) can be specified as XA’,

BC’, DE’, and HL’, thus providing up to eight 8-bit registers. The XA register pair functions as an 8-bit

accumulator which performs transfers, arithmetic/logical operations, comparisons, and increments/

decrements of 8-bit data. The other register pairs perform transfers, arithmetic/logical operations,

comparisons, and increments/decrements with the accumulator. The HL register pair functions mainly

as a data pointer, and the DE and DL register pairs function as an auxiliary data pointer.

Examples 1.

INCS

; HL <– HL + 1, skip at HL = 00H

ADDS

XA,BC

; XA <– XA + BC, skip at carry

SUBC

DE’,XA

; DE’ <– DE’ – XA – CY

MOV

XA,XA’

; XA <– XA’

MOVT

XA,@PCDE

; XA <– (PC

12-8

+ DE) ROM, reference table

SKE

XA, BC

; Skip if XA = BC

2. The value of the count register (T0) for timer/event counter 0 is tested until it becomes

greater than the value of the BC’ register pair.

CLR1

MBE

NO:

MOV

XA,T0

; Read count register

SUBS

XA,BC’

; XA • BC?

YES

; YES

; NO