Description:

Pop the top two bytes off the stack as an IO port reference and then pop the top byte from the stack into that IO port.

Pseudo Code:

portRef = stack[sp - 2]
byteVal = stack[sp - 3]
port[portRef] = byteVal
sp = sp - 3
pc = pc + 1

Flags Affected:

D	H	C	Z	N

Possible Errors:

tvmStackUnderflow	-	There were not enough bytes in the stack to get the I/O Port reference or the data byte.
tvmStackIOErr	-	The write operation to the memory-mapped IO port is invalid.

Example:

popbmx

Here the address for the aPortVMTimer port (0x0000) is on top of the stack (as an unsigned short) we write the delay byte (0x03) to this timer port.

Before stack   top 1 0x00 2 0x00 3 0x03 4 0x32 5 0x02   bottom

After stack   top 1 0x32 2 0x02   bottom