Z86C72 Datasheet, PDF (33/71 Pages) Zilog, Inc. – IR MICROCONTROLLER

Zilog
Z86C72/C92/L72/L92
IR Microcontroller
R253 RP
D7 D6 D5 D4 D3 D2 D1 D0
Default Setting After Reset = 0000 0000
Expanded Register File Pointer
Working Register Pointer
Note: When SPH is used as a general-purpose register
and Port 0 is in address mode, the contents of SPH will be
1 ^{loaded into Port 0 whenever the internal stack is accessed.}
r7 r6 r5 r4 r3 r2 r1 r0 _R253
Figure 20. Register Pointer
Register File. The register file (bank 0) consists of four I/O
port registers, 236 general-purpose registers, and 16 con-
trol and status registers (R0-R3, R4-R239, and R240-
R255, respectively), Plus two expanded registers groups
(Banks D and F). Instructions can access registers directly
or indirectly through an 8-bit address field. This allows a
short, 4-bit register address using the Register Pointer
(Figure 23). In the 4-bit mode, the register file is divided
into 16 working register groups, each occupying 16 contin-
uous locations. The Register Pointer addresses the start-
ing location of the active working register group.
Note: Working register group E0-EF can only be access-
ed through working registers and indirect addressing
modes.
Stack. The Z86L/CX2 external data memory or the inter-
nal register file is used for the stack. An 8-bit Stack Pointer
(R255) is used for the internal stack that resides in the gen-
eral-purpose registers (R4-R239). SPH is used as a gen-
eral-purpose register only when using internal stacks.
The upper nibble of the register file address
provided by the register pointer specifies
the active working-register group
FF
R15 to R0
F0
Specified Working
Register Group
2F
20
1F
Register Group 1
10
0F
Register Group 0
00
I/O Ports
The lower nibble
of the register
file address
provided by the
instruction points
to the specified
register
R15 to R0
R15 to R4
R3 to R0
Figure 21. Register Pointer
DS97LVO0900
PRELIMINARY
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