9. Data transfer
A CPU, in order to process data, needs to move that data around. This includes moving data between its internal registers and it includes moving data in an out of external RAM.
A number of mnemonic commands support this movement of data
|MOV||Move (copy)||MOV dest, source||
dest = source,
source remains source
|PUSH||Place item on to the stack||PUSH source||stack contain source|
|POP||Get item from stack||POP dest||get item from stack|
|XCHG||Swap around||XCHG dest,source||
dest = source
source = dest
|IN||Input from a port||IN dest, port||dest = data at port|
|OUT||Output to a port||OUT port, source||port = content or source|
The MOV command may include a number of variants within the full instruction set, but it basically copies data from one location to another.
The PUSH and POP operations are the commands that control the contents of the stack. The stack is used to control subroutine calls and returning from subroutines.
A CPU may have a number of 'ports'. A port is one or more physical pins on the chip assigned to handling data moving into and out of the chip.
For example a serial port or an 8 bit data port may be available on the chip. CPUs especially developed for control purposes have many complicated ports, for example an automotive engine management CPU.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: control CPUs
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