H/W 2: Timer (8253) and Interrupts
Introduction:
In
this experiment we will be using 8253 timer IC and two interrupts (5.5 and 7.5)
available on the 8085. Study the material on Interrupts and on 8253 in the text
book.
Problems:
1. Design the timer part of the circuit to generate 1kHz square wave using timer 2 in mode 3.Choose proper count and clock frequency. Timer 0 and timer 1 are used by the kit, so are not available. Use RST7.5 (with the help of de-bounce key ) to toggle the frequency between 1 kHz and 2 kHz.
2. Change the mode and count of the timer to generate 1 second narrow pulses using mode 2. Connect this pulse output to RST 5.5 after inversion. Write an ISR for RST 5.5 to update a 12 hr. clock of the form HH:MM:SS. The time should be displayed on the 7 segment display of the kit .
3. Write an ISR such that when RST 7.5
key is pressed the display shows the date in the DDMMYY format for
approximately 3 seconds. During the display of the date, the clock should not
lose time.
Demonstrate the working
of above programs.
Note:
The interface unit has following
connections available:
1)
Terminals for 8253 timer 2
2) Clockout (1.785 MHz), Clockout / 2, Clockout / 100.
3)
Input and output for 2 digital inverters
74LS04
4) Interrupts 5.5 ,7.5 and INTR.
5) 2 de-bounce switches.
6) + 5 volt and ground
Pictures:
1) Setup
2) Module