Z86L79 Datasheet, PDF (21/58 Pages) Zilog, Inc. – Low-Voltage Microcontroller

Z86L79/80
Low-Voltage Microcontroller
FUNCTIONAL DESCRIPTION (Continued)
R253 RP
D7 D6 D5 D4 D3 D2 D1 D0
Zilog
Note: When SPH is used as a general-purpose register
and Port 0 is in address mode, the contents of SPH will be
loaded into Port 0 whenever the internal stack is accessed
Default Setting After Reset = 0000 0000
Expanded Register
File Pointer
Working Register
Pointer
Figure 16. Register Pointer
Register File. The register file consists of four I/O port reg-
isters, 236 general-purpose registers with 10 control and
status registers (R3-R0, R239-R4, and R255-R246, re-
spectively), plus three Expanded Register Groups (0, D,
and F) which reside in the expanded register group. In-
structions 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 14). In
the 4-bit mode, the register file is divided into 16 working
register groups, each occupying 16 continuous locations.
The Register Pointer addresses the starting location of the
active working register group.
Note: Register Bank E0-EF is only accessed through
working registers and indirect addressing modes. R240-
R245 registers are reserved.
Stack. The Z86L7X external data memory or the internal
register file is used for the stack. An 8-bit Stack Pointer
(R255) is used for the internal stack that resides within the
general-purpose registers (R4-R239). SPH is used as a
general-purpose register only when using internal stacks.
r7 r6 r5 r4
r3 r2 r1 r0 _R253
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 17. Register Pointer
3-21
PRELIMINARY
DS97LVO0601