Intel 8080 - RLA

RAL
Chapter 3. Instruction Set
Stack Stack
Before
PUSH
Address
After PUSH
SP before ..
xx 9AAF xx
xx
9AAE 2A
xx 9AAD 4C
...
SP after
xx
9AAC xx
PUSH PSW
PUSH PSW copies the Program Status Word onto the stack. The Program Status Word comprises the contents
of the accumulator and the current settings of the condition flags. Because there are only five condition flags,
PUSH PSW formats the flags into an eight-bit byte as follows:
7 6 543 2 0
~S~_z~_o~I_AC_I_o~l_p~~I~c_Y~l
On the 8080, bits 3 and 5 are always zero; bit one is always set to one. These filler bits are undefined on the
8085.
PUSH PSW decrements the stack pointer by one and copies the contents of the accumulator to the resulting
address.
PUSH PSW again decrements the pointer and copies the formatted condition flag byte to the resulting
address. The contents
of the accumulator and the condition flags remain unchanged.
Cycles:
States:
Addressing:
Flags:
Example:
o
o
2J
3
11 (12 on 8085)
register indirect
none
When a program calls subroutines, it is frequently necessary to preserve the current program status so the calling
program can continue normally when
it regains control. Typically, the subroutine performs a PUSH PSW prior to
execution of any instruction that might alter the contents of the accumulator or the condition flag settings.
The subroutine then restores the pre-call system status
by executing a POP PSW instruction just before returning
control
to the calling program.
ROTATE LEFT THROUGH CARRY
RAL rotates the contents of the accumulator and the carry flag one bit position to the left. The carry flag, which
is treated as though it were part of the accumulator, transfers to the low-order bit of the accumulator. The high-
order bit of the accumulator transfers into the carry flag.
Opcode
Operand
RAL
Operands are not permitted with the RAL instruction.
345