Experiment 5 -- Parallel I/O and Timer/Count Interface

        On this two week, I had done the lab 5. The objective of Lab 5 is to study the interfacing of the 8255 PPI and 8254 PTC with the 8088 MPU. First of all, I need to wrap wire the control signals of the 8255 PPI and 8254 PTC as shown in the figure below.

         This is a very interesting hand work. After that, I have to write my own assembly program for the certain result. Once the switch button is pressed, the buzzer will be activated with a 1-KHz signal for a duration of around 0.5 seconds and all LEDs are turned on. If the button is pressed again, the all LEDs are turned off.

For verifying that I had generated 1-KHz signal, I used oscilloscope to see the output signal’s frequency as the below figure.

Here is the part of assembly program which set 1 KHz signal's frequency.

timer_1KHz_msb     equ     9   timer_1KHz_lsb     equ     196 ;When the switch is pressed, LEDs change state and sound 0.5 second. EXAMPLE1   PROC  NEAR       ;call  ram_test     ; Initialize the 8255 in mode 0     mov dx,i8255_base_address       mov al,10010000B ;set PA as input, set PB as output, set PC as output       inc dx       inc dx       inc dx                  ;point to command register       out dx,al        ;end initialize the 8255        ; Initialize the 8254 in mode 3     mov     al,00110110B       mov     dx,i8254_base_address       inc     dx       inc     dx       inc     dx       ;point to command register       out     dx,al       mov     dx,i8254_base_address       mov     al,timer_1KHz_lsb       out     dx,al       mov     al,timer_1KHz_msb       out     dx,al        ;end initialize the 8254

  To calculation of the value in MSB and LSB for generating 1 KHz

We know that the period of 1 KHz signal is 1ms. The period of a 2.5MHz clock signal is 0.4us. Therefore, the number of count for the counter is 0.5ms/0.4us= 9*256+196

Thus, MSB is 9 and LSB is 196.

This is a very interesting and meaningful lab. As this lab course is related to ELEG323 0(Microprocessors and computer systems). I have to use the knowledge that I have learnt in ELEG3230 to the lab. I feel proud of me that I can apply those things into the lab.