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eZ8

™

CPU Core

User Manual

UM012820-0810 DECW Instruction

138

Attributes

Escaped Mode Addressing

Using Escaped Mode Addressing, address modes RR can specify a work-

ing register Pair or IR can specify a working register. If the high nibble of

the source or destination address is

Eh (1110b), a working register (or

Pair) is inferred. For example, if Working Register Pair R12 and R13

(with base address

Ch) is the preferred destination operand, use ECh as the

destination operand in the Op Code. To access Register Pairs with

addresses

E0h to EFh, either set the Working Group Pointer, RP[7:4], to

Eh or use indirect addressing.

Sample Usage

If Register Pair 30h and 31h contain the value 0AF2h, the following

statement leaves the value

0AF1h in Register Pair 30h and 31h and clears

the Z, V, and S flags:

DECW

30h

Object Code: 80 30

If Working Register R0 contains 30h and Register Pair 30h and 31h con-

tain the value FAF3h, the following statement leaves the value FAF2h in

30h and 31h, sets the S flag, and clears the. Z and V flags:

DECW @R0



Object Code: 81 E0

Mnemonic Destination

Code

(Hex) Operand 1 Operand 2 Operand 3

DECW RR1 80 RR1 — —

DECW @R1 81 R1 — —

1 2 ... 148 149 150 151 152 153 154 155 156 157 158 ... 313 314

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