MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
875
Preliminary—Subject to Change Without Notice
.” V Flag is calculated using ALU adder output (i.e., it is not affected by 1-bit shift/rotate
operations).
Zero Flag (Z)
Zero flag equal to 1 indicates that the result from the ALU, limited to the operation size, is zero, regardless
of the operation performed, whether the result is written, or where it is written. It depends on the operation
size, as shown in
23.4.8.2.2
ALU ADD Operation with and without shifting
ADD operation is selected by ALUOP or ALUOPI fields and when none of them is available in a
microinstruction format
1
. Optionally, result can be shifted or rotated right by 1 bit, which is selected by
SHF, ALUOP or ALUOPI fields. See
Section 23.4.9, “Microinstruction Set
” for more details.
describes how CIN and BINV fields change ADD operation behavior.
Table 23-42. Overflow Flag on Addition
1
- V
1
for V-flag definition on the absolute operation, see
Section 23.4.8.2.8, “Absolute Value
.
Op. Size
Value
2
2
BS is taken after any inversion by the BINV field, but not added to the carry bit (CIN field)
8 bits
(AS[7] & BS[7] & !alu_adder_output[7]) | (!AS[7] & !BS[7] & alu_adder_output[7])
16 bits
(AS[15] & BS[15] & !alu_adder_output[15]) |
(!AS[15] & !BS[15] & alu_adder_output[15])
24 bits
(AS[23] & BS[23] & !alu_adder_output[23]) |
(!AS[23] & !BS[23] & alu_adder_output[23])
Table 23-43. Zero Flag - Z
Operation Size
Value
8 bits
Z = (result[7:0] == 0x00)
16 bits
Z = (result[15:0] == 0x0000)
24 bits
Z = (result[23:0] == 0x000000)
1.
ALU operations only occur on formats where a destination field is found (T2ABD/T2D).
Table 23-44. Types of ADD operations
BINV
CIN
Operation (adder output)
1
1
AS + BS
1
0
AS + BS + 1
0
0
AS - BS
0
1
AS - BS - 1