MGMT 1040 Lecture Notes - Lecture 3: Peripheral, Memory Address Register, Memory Buffer Register
8 May 2018
School
Department
Course
Professor
MGMT 1040 Tutorial 3 Notes – I/O Operation
Introduction
• The I/O operation is similar to that of the Little Man Computer.
• Input from the peripheral device is transferred from the I/O module or buffer for that
peripheral device one word at a time to the I/O data register and from there to an
accumulator register under program control, just as occurred in the Little Man
Computer.
• Similarly, individual words of output data pass from an accumulator register to the I/O
data register where they can be read by the appropriate I/O module, again under
program control.
• Each instruction produces a single input or output.
• This method is known as programmed I/O.
• In practice, it is most likely that there will be multiple devices connected to the CPU.
• Since each device must be recognized individually, address information must be sent
with the I/O instruction.
• The address field of the I/O instruction can be used for this purpose.
• An I/O address register in the CPU holds the address for transfer to the bus.
• Each I/O module will have an identification address that will allow it to identify I/O
instructions addressed to it and to ignore other I/O not intended for it.
• As has been noted, it is common for an I/O module to have several addresses, each of
which represents a different control command or status request
• Which addresses a different device when a particular module supports multiple devices.
• For example, the address field in the Little Man input and output instructions could be
used to address up to a combination of one hundred devices, status requests, or control
commands.
• The concept of programmed I/O.
• Indeed, the LMC uses the address field to select the I-basket (901) or O-basket (902) as
the I/O device within the 900 instruction.
find more resources at oneclass.com
find more resources at oneclass.com
