16-bit Input Port & Printer Interface for FALCON-A CPU, Slides of Computer Architecture and Organization

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Problem Statement:

Design a 16-bit parallel input port

mapped on address 7Eh of the I/O

space of the FALCON-A CPU.

• The address in this case is 7Eh.
• The address decoder has the

inputs A7 and A0 inverted.

• Control bus signal IOR# is used

instead of the signal IOW#.

Differences

A 16-bit Parallel Input Port for

the FALCON-A at Address

7Eh and 7Fh

Design#

Given a FALCON-A processor with a 16-

bit parallel input port at address 7Eh and a

16-bit parallel output port at address DEh.

Sixteen LED branches are used to display

the data at the output port and sixteen

switches are used to send data through

the input port. Write an assembly

language program to continuously monitor

the input port and blink the LED or LED(s)

corresponding to the switch(es) set to

logic 1.

• After the second wait, the

program reads the input port

again.

• The LEDs that will be turned on

according to the new switch

settings at the input port.

• The process repeats indefinitely.

• It is also possible to use a

single address for both the

input and the output port.

• This can be done with the help

of a decoder.

Example

FALCON-A’s Address

Decoder for an I/O Port at

Address 2Ch

• The address decoder uses the

addresses 00DEh and 00DFh of the

FALCON-A’s memory space.

• Use the store instruction instead of

the out instruction for sending the

data to the output port.

Disadvantage

• The address decoder will become

more complex, resulting in

increased hardware costs.