NATIONAL TAIWAN OCEAN UNIVERSITY 國立台灣海洋大學 2002/4/8 Microcomputers and...

2002/4/82002/4/8 Microcomputers and MicroprocessorMicrocomputers and Microprocessorss

NATIONAL TAIWANNATIONAL TAIWAN

OCEAN UNIVERSITYOCEAN UNIVERSITY國立台灣海洋大學國立台灣海洋大學

Chapter 9Chapter 9COUNTER/TIMER COUNTER/TIMER PROGRAMMING IN THE 8051PROGRAMMING IN THE 8051

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OutlinesOutlines

List the timers of the 8051 and their associated List the timers of the 8051 and their associated registersregisters

Describe the various modes of the 8051 timersDescribe the various modes of the 8051 timers Program the 8051 timers to generate time delaysProgram the 8051 timers to generate time delays Program the 8051 counters as event countersProgram the 8051 counters as event counters

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PROGRAMMING 8051 TIMERSPROGRAMMING 8051 TIMERS

Timer 0 registersTimer 0 registersTL0 ( timer 0 low byte )TH0 ( timer 0 high byte )

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Timer 1 registersTimer 1 registersTL1 ( timer 1 low byte )TH1 ( timer 1 high byte )

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TMOD (timer mode) registerTMOD (timer mode) register

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Mode 1 programmingMode 1 programming

1.Loaded value into TL and TH2.”SETB TR0” for timer 0 ;”SETB TR1” for timer 13.If TF (timer flag) = high “CLR TR0” or “CLR TR1”4.Reloaded TH and TL value, TF reset to 0

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Steps to program in mode 1Steps to program in mode 1

1.Load the TMOD value2.Load registers TL and TH 3.Start the timer (SETB TR0 or SETB TR1)4.Keep monitoring the timer flag (TF)5.Stop the timer (CLR TR0 or CLR TR1)6.Clear the TF flag7.Go back to step 2

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Calculate Timer DelayCalculate Timer Delay

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Finding values to be loaded into the timerFinding values to be loaded into the timer

Assuming XTAL =11.0592MHz from Example 9-10

1.Divide the desired time delay by 1.085μs2.Perform 65536-n, where n is the decimal value we got in Step 13.Convert the result of Step 2 to hex, where yyxx is the initial hex value to be loaded into the timer’s registers4.Set TL = xx and TH = yy

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Mode 0Mode 0Like mode 1 except that it is a 13-bit timer

Mode 2 ProgrammingMode 2 Programming

1.Loaded value into TH (8-bit timer)2.”SETB TR0” for timer 0 ;”SETB TR1” for timer 13.If TF (timer flag) = high “CLR TR0” or “CLR TR1”4.Reloaded TL value kept by TH

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Steps to program in mode 2Steps to program in mode 2

1.Load the TMOD value2.Load the TH registers 3.Start the timer4.Keep monitoring the timer flag (TF)5.Clear the TF flag7.Go back to step 4

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C/T bit in TMOD registerC/T bit in TMOD register

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The case of GATE =1 in TMODThe case of GATE =1 in TMOD

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