Zilog Z86193 - Manual (Page 13)

Z8
®
CPU
User Manual
UM001604-0108 Address Space
6
Registers can be accessed as either 8-bit or 16-bit registers using Direct, Indirect, or
Indexed Addressing. All 236 general-purpose registers can be referenced or modified by
any instruction that accesses an 8-bit register, without the requirement for special instruc-
tions. Registers accessed as 16 bits are treated as even-odd register pairs (there are 118
valid pairs). In this case, the data’s most significant byte (MSB) is stored in the even num-
bered register, while the least significant byte (LSB) goes into the next higher odd num-
bered register. See
Figure 2 .
By using a logical instruction and a mask, individual bits within registers can be accessed
for bit set, bit clear, bit complement, or bit test operations. For example, the instruction
AND R15, MASK performs a bit clear operation,
Figure 3 on page 7 displays this
example.
F4 T0 Timer/Counter 0
F3 PRE1 T1 Prescaler
F2 T1 Timer/Counter 1
F1 TMR Timer Mode
F0 SIO Serial I/O
EF R239
General-Purpose Registers (GPR)
04 R4
03 P3 Port 3
02 P2 Port 2
01 P1 Port 1
00 P0 Port 0
Figure 2. 16-Bit Register Addressing
Table 2. Z8 Standard Register File (Continued)
Hex Address
Register
Identifier Register Description
MSB LSB
Rn Rn+1
n = Even Address