Description:

Pop the top two bytes off the stack as a I/O port reference.  Read a short from the referenced port and push it onto the stack.

Pseudo Code:

portRef = stack[sp - 2]
sp = sp - 2
stack[sp] = (short)port[portRef]
sp = sp + 2
pc = pc + 1

Flags Affected:

D	H	C	Z	N

Possible Errors:

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

Example:

pushmsx

Here the address for the aPortA2DValue0 port (0x0480) is on top of the stack (as an unsigned short) and we read the analog value (0x0323 in this example) as a short and push it onto stack.

Before stack   top 1 0x80 2 0x04 3 0xAA 4 0x32 5 0x02   bottom

After stack   top 1 0x23 2 0x03 3 0xAA 4 0x32 5 0x02   bottom