Zilog Z8F0130 Manual de usuario descargar pdf (Pagina 198)

eZ8

™

CPU Core

User Manual

UM012820-0810 LDX Instruction

183

If the high byte of the source or destination address is EEh (11101110b),

a working register is inferred. For example, the operand

EE3h selects

Working Register R3. The full 12-bit address is provided by

{RP[3:0],

RP[7:4], 3h}

To access registers on Page

Eh (addresses E00h to EFFh), set the Page

Pointer, RP[3:0], to

Eh and set the Working Group Pointer, RP[7:4], to

the preferred Working Group.

.ER Notation

The .ER notation is used with Op Codes 87h and 97h, to distinguish

between these two cases, which might otherwise be ambiguous. The

potential ambiguity arises because in both these Op Codes, the two oper-

ands are both indirect registers, to be prefixed with the @ symbol. How-

ever, one of these is to be treated as an indirect Register Pair, which are

combined to give a 16-bit address, while the other is to be treated as a sin-

gle register which yields an 8-bit address. Without some way of distin-

guishing between the two cases, it would be impossible for the assembler

to determine whether the user’s purpose was to treat the destination oper-

and as a Register Pair and the source as a single register, or vice versa.

The

.ER notation resolves this ambiguity. The operand which is prefaced

with

.ER is taken to be a Register Pair, and the other is treated as a single

Codes 87 and 97 in the Sample Usage section.

Sample Usage

If Register 702h contains the value B3h, the following statement loads

the value

B3h into Working Register R1:

LDX R1, 702h

Object Code: 84 17 02

The contents of register 702h are not affected.

1 2 ... 193 194 195 196 197 198 199 200 201 202 203 ... 313 314

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Zilog Z8F0130 Manual de usuario Pagina 198