| Back to Victorian University Electronics Intranet Home Page Mirror. |
It is possible to use the same hardware used to interface an AT89C2051 micro-controller to switches and leds to interface them to a computer via the parallel port.
Photo showing switches and leds interfaced to a computer parallel port
using a DT004 & DT203.
Switches and leds interfaced using the sample program below. The keyboard
character enter is a '1', there the binary as shown by the leds is '10001100'
LSB to MSB.
Sample 8088 program to drive leds and read a switch.
;Written by Peter Averill 13-5-1999
;Sample program to output the ascii value of a key pressed at the
;k/b in binary on leds connected to a parallel port. The program
;will continue in a loop until a switch connected to the ACK line
;on the parallel port is pressed. Tested using a Dontronics DT004
;& DT203 boards (see photo). The top left push button switch
is
;connected to the ACK line. This is D8 on the Simmbus.
There are
;5 inputs on the status port of the parallel port (base address + 1)
;that can be wired to switches. In the example I have only connected
;the one switch.
;Because DOS waits for a key to be pressed, to exit the program
;you need to press the switch connected to the ACK line and press
;a key on the keyboard. The ACK line can also be used to generate
;an interrupt.
port equ 0278h
;lptx base address
ack_active equ 03fh
.model small
;----------------------------------------------------------
.stack 20h
;----------------------------------------------------------
.data
;----------------------------------------------------------
.code
main proc far
push ds
;Push DS onto stack
sub
ax,ax ;Push zero offset
push ax
; onto stack
mov
ax,_data ;setup
mov
ds,ax ;data segment address
top: call get_key
mov
dx,port
out
dx,al
inc
dx
in
al,dx
cmp
al,ack_active
jne
top
ret ;Return to DOS
main endp
;-------------------------------------------------------------
get_key proc near
mov
ah,01
int
21h
ret
get_key endp
;--------------------------------------------------------------
end
main
| Back to Victorian University Electronics Intranet Home Page Mirror. |
DonTronics Links:
| Home | Products | Prices | Directory | Order | Contact | New | Books | Files | Links | FAQ |