ZiLOG Z08617 Manual page 11

FUNCTIONAL DESCRIPTION (Continued)
Register File. The register file (Figure 10) consists of four
I/O port registers, 124 general-purpose registers and 16
control and status registers (R3-R0, R127-R4, and R255-
R240, respectively). The instructions can access registers
directly or indirectly through an 8-bit address field. This
allows short, 4-bit register addressing using the Register
LOCATION
R255
Stack Pointer (Bits 7-0)
R254
General-Purpose Register (Bits 7-0)
R253
Register Pointer
R252
Program Control Flags
R251
Interrupt Mask Register
R250
Interrupt Request Register
R249 Interrupt Priority Register
R248
Ports 1-0 Mode
R247
Port 3 Mode
R246
Port 2 Mode
R245
T0 Prescaler
R244
Timer/Counter0
R243
T1 Prescaler
R242
Timer/Counter1
R241
Timer Mode
R240
Reserved
Not Implemented
R127
General-Purpose
Registers
R4
R3
R2
R1
R0
Figure 10. Register File Configuration
IDENTIFIERS
SPL
GPR
RP
FLAGS
IMR
IRQ
IPR
P01M
P3M
P2M
PREQ
T0
PRE1
T1
TMR
P3
Port 3
P2
Port 2
P1
Port 1
P0
Port 0
Pointer (Figure 11). In the 4-bit mode, the register file is
divided into nine working-register groups, each occupy-
ing 16 continuous locations. The Register Pointer ad-
dresses the starting location of the active working-register
group.
r7 r6 r5 r4
The upper nibble of the register file address
provided by the register pointer specifies
the active working-register group.
FF
Register Group F
F0
•
•
•
•
•
•
•
•
•
•
Specified Working
•
Register Group
2F
20
1F
Register Group 1
10
0F
Register Group 0
I/O Ports
00
Figure 11. Register Pointer Configuration
®
Z08617 NMOS Z8 8-B
IT
K C
EYBOARD ONTROLLER
r3 r2 r1 r0 R253
(Register Pointer)
R15 to R0
•
•
•
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
MCU
11