03-08-2013, 02:45 PM
INTERFACING 8253 (TIMER IC) WITH 8085 PROCESSOR
AIM:
To interface 8253 Programmable Interval Timer to 8085 and verify
of 8253 in six different modes.
the operation
APPARATUS REQUIRED:
8085 Microprocessor toolkit.
8253 Interface board.
VXT parallel bus.
Regulated D.C power supply.
CRO.
MODE 0-Interrupt On Terminal Count:-
The output will be initially low after mode set operation. After loading the counter, the
output will remain low while counting and on terminal count, the output will become high
until reloaded again.
Let us see the channel in mode0. Connect the CLK 0 to the debounce circuit and
execute the following program.
MODE 1-Programmable One Shot:-
After loading the count, the output will remain low following the rising edge of the
gate input. The output will go high on the terminal count. It is retriggerable; hence the
output will remain low for the full count after any rising edge of the gate input.
MODE 2-Rate Generator:
It is a simple divide by N counter. The output will be low for one period of the input
clock. The period from one output pulse to next equals the number of input count in the
count register. If the count register is reloaded between output pulses, the present period will
not be affected, but the subsequent period will reflect a new value.
MODE 3-Square Generator:
It is similar to mode 2 except that the output will remain high until one half of the
count and goes low for the other half provided the count is an even number. If the count is
odd the output will be high for (count +1)/2 counts. This mode is used for generating baud
rate of 8251.