Z8F6421PM020SC Datasheet, PDF (272/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
252
Flags Register
The Flags Register contains the status information regarding the most recent arithmetic,
logical, bit manipulation or rotate and shift operation. The Flags Register contains six bits
of status information that are set or cleared by CPU operations. Four of the bits (C, V, Z
and S) can be tested for use with conditional jump instructions. Two flags (H and D) can-
not be tested and are used for Binary-Coded Decimal (BCD) arithmetic.
The two remaining bits, User Flags (F1 and F2), are available as general-purpose status
bits. User Flags are unaffected by arithmetic operations and must be set or cleared by
instructions. The User Flags cannot be used with conditional Jumps. They are undefined at
initial power-up and are unaffected by Reset. Figure 58 illustrates the flags and their bit
positions in the Flags Register.
Bit
Bit
7
0
C Z S V D H F2 F1 Flags Register
U = Undefined
Figure 58. Flags Register
User Flags
Half Carry Flag
Decimal Adjust Flag
Overflow Flag
Sign Flag
Zero Flag
Carry Flag
Interrupts, the Software Trap (TRAP) instruction, and Illegal Instruction Traps all write
the value of the Flags Register to the stack. Executing an Interrupt Return (IRET) instruc-
tion restores the value saved on the stack into the Flags Register.
PS019915-1005
eZ8 CPU Instruction Set