Z86C03 Datasheet, PDF (27/348 Pages) Zilog, Inc. – General-Purpose Register File. Flexible I/O. Analog Inputs

Z8 CPU
User Manual
9
referenced or modified by any instruction that accesses an 8-bit register,
without the requirement for special instructions. 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
numbered register, while the Least Significant Byte (LSB) goes into the
next higher odd numbered register. See Figure 2.
MSB
LSB
Rn Rn+1
n = Even Address
Figure 2. 16-Bit Register Addressing
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 opera-
tions. For example, the instruction AND R15, MASK performs a bit clear
operation. Figure 3 shows this example.
0 1 1 1 0 0 0 0 ^R15
1 1 0 1 1 1 1 1 ^MASK
AND R15, DFh ;Clear Bit 5 of Working Register 15
0 1 0 1 0 0 0 0 ^R15
Figure 3. Accessing Individual Bits (Example)
UM001602-0904
Address Space