Programmable Interval Timer

T.Shakeel, Lovely Professional University.

IC 8254 is an programmable interval Timer, whose function is similar to software program(counter and Time delay).Applications are Used to generate time delayClock pulsesSquare wave generators and etc

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

8254 consists of 3- 16 bit counters, which works individually.This counters operates in 6 different modes8254 is a 24 pin dual in line package ICIt requires +5v power supply.To operate as an counter, 16 bit count value is to be stored in register and required command should be given to start the decrement operation When the count is decrement to zero, and signal is given to MPU( consider as a interrupt).We can also read the contents of counter while its value is decrementing.

T.Shakeel, Lovely Professional University.

8254 consists of 3 individual counter register(0,1,2).Data bus (D7-D0)R/W control logicControl register

Counter is having 2 input pins and one output pin.Input pins: CLOCK(CLK) and GATEOutput Pins: OUTData pins are connected to the data bus pins of MPU

T.Shakeel, Lovely Professional University.

In 8254 , 5 control logic pins are present RD(AL): WR(AL):RD and WR control lines are connected with IOM, IOR, MEMR and MEMW control lines of MPU.CS(AL): This pins is used to Disable and enable the 8254 chip and this is done by decoding the address linesA1,A0: This lines are used to select the 3 different counter.

T.Shakeel, Lovely Professional University.

Each counter is assigned with individual port address.Control register is Common to all counters and has its own port address.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

8254 can be programmed to provide various types of output through write operation and we can also check the count while counting through Read operation.

Write Operation:To initialize a Counter, following steps are requiredWrite a control word into control registerLoad the low-order byte of count in the counter registerLoad the high-order byte of count in the counter registerRead Operation:This operation can be done in 2 ways:Reading the count after stopping the counter Second method involves reading a count, while count is in progress( READING ON FLY).

T.Shakeel, Lovely Professional University.

Mode 0 Interrupt on terminal countMode 1Programmable one-shotMode 2Rate GeneratorMode 3 Square wave rate generatorMode 4Software triggered strobeMode 5Hardware trigger strobe

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

T.Shakeel, Lovely Professional University.

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