Z86C30 datasheet(29/348 Pages) ZILOG

29 / 348 page

Z8 CPU

User Manual

UM001602-0904

Address Space

registers are known as Working Registers. A Register Pointer (one of the

control registers, FDh) contains the base address of the active Working

current Working Register Group.

When accessing one of the Working Registers, the 4-bit address of the

Working Register is combined within the upper four bits (high nibble) of

the Register Pointer, thus forming the 8-bit actual address. Figure 4 illus-

trates this operation. Because working registers are typically speciﬁed by

short format instructions, there are fewer bytes of code required, which

reduces execution time. In addition, when processing interrupts or chang-

ing tasks, the Register Pointer speeds context switching. A special Set

Pointer.

Table 3. Working Register Groups

(FDh) High Nibble

Working Register

Group (Hex)

Actual Registers

(Hex)

1111b

F0–FF

1110b

E0–EF

1101b

D0–DF

1100b

C0–CF

1011b

B0–BF

1010b

A0–AF

1001b

90–9F

1000b

80–8F

0111b

70–7F

0110b

60–6F

0101b

50–5F

0100b

40–4F

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