Propeller Manual

3: Assembly Language Reference – Effects (WC, WZ, WR, NR)
Effects ( WC, WZ, WR, NR )
Every Propeller Assembly instruction has an optional “effects” field that causes it to modify a
flag or register when it executes. The basic syntax for Propeller Assembly instructions is:
〈Label〉 〈Condition〉 Instruction Operands 〈Effects〉
The optional Effects field can contain one or more of the four items shown below. For any
effect not specified next to the instruction in code, the default behavior remains as indicated
by the corresponding bit (Z, C, or R) in the
ZCRI field of the instruction’s opcode.
Table 3-2: Effects
Effect Description
WC Updates C Flag. See WC, page 372.
WZ Updates Z Flag. See WZ, page 377.
WR Updates Destination Register. See WR, page 373.
NR Preserves Destination Register. See NR, page 325.
Follow an instruction with one to three comma-delimited Effects to cause that instruction to
affect the indicated item. For example:
and temp1, #$20 wc
andn temp2, #$38 wz, nr
if_c_and_z jmp #MoreCode
The first instruction performs a bitwise AND of the value in the temp1 register with $20,
stores the result in
temp1 and modifies with C flag to indicate the parity of the result. The
second instruction performs a bitwise AND NOT of the value in the
temp2 register with $38,
modifies the Z flag according to whether or not the result is zero, and does not write the result
to
temp2. During the execution of the first instruction, the Z flag is not altered. During the
execution of the second instruction, the C flag is not altered. If these instructions did not
include the
WC and WZ effects, those flags would not be altered at all. The third instruction,
which specifies a Condition, jumps to the
MoreCode label (not shown) but only if both the C
and Z flags are set; otherwise, the
JMP instruction acts like a NOP instruction.
Using Effects on instructions, along with Conditions on later instructions, enables code to be
much more powerful than what is possible with typical assembly languages. See
IF_x
(Conditions) on page 295 for more information.
Propeller Manual v1.1 · Page 291