programmable interval timer
TRANSCRIPT
Programmable Interval Timer8253
By,Daggubati.Sirisha
• The Intel 8253 and 8254 are Programmable Interval Timers (PITs), which perform timing and counting functions. They were primarily designed for the Intel 8080/8085-processors, but later used in x86-systems.
• There are several applications where we need to generate clock signals of different frequency, Delays of different duration and strobe signals after certain interval
• These Signals can be generated by using different techniques
• Software,Hardware and combined • Programmable interval Timer is used in
Software based approachClock
using 2 delay routine we generateclock
Generating delay
Strobe signal
Limitation
Some application e need to generate clock and delay at a time , which is not possible using this method, although it is Flexible to generate everything by program ,due to above Drawback
Hardware based approach
Hardware based approach
555 Timer
Drawback:If we need to change the frequency of clock need to change the capacitor andResistor values ie hardware need to be changed, so we go for combined approach
trigger
Combined approach-Programmable Interval Timer-8253
Max clk freq 2mhz
8253
• Control word register used to control mode of operation
• three16 bit registers called Counters used to generate delay, clock signal and strobe signal
Addressing and CONTROL REGISTER
Interrupt on TC-Mode-0
Count down can be inhibited
Gate is inhibiting the clock to decrement the count
Mode:1(Monostable multivibrator)
When trigger is applied it will start count, here gate line acts like trigger input
Rate generator
If u write n ,it keeps gnerating strobe after tc reaches 0-called rate generatorGate input used to load reset,the count value reset and start from n value
Square wave generator
Output will remain high or low for this durationDifference of period is only one clock cycle between odd and even number
Softare triggered strobe
It generate the strobe at the output, here write operation acts as the triggerOperation can be delayed by gating
Hardare triggered strobe
This gate line is used as the trigger input, count down is initiated by gate