ECE473/573Microprocessor System Design, Dr. Shiue 1Timer and CounterECE473/573Microprocessor System Design, Dr. Shiue 2Timer and Counter• Timer and Counter– Measure the time/frequency of input signal. – Generate outputs with variable frequency and pulse width. – Can be controlled with software. – Can be accessed thru interrupt and software. • Structure of Timer/Counter (a series of divide-by-two flip flop:) • 4 bit counterECE473/573Microprocessor System Design, Dr. Shiue 3Timer and Counter• Not a power of 2 multiple of the clock freq. – Q1: Count-by-10 counter• Timer: when the incoming clock frequency is known. – Get clock from Oscillator frequency (1/12), then by setting the pre-load value. We can generate a fixed period of time known to the designers. • Counter: when the incoming clock is ‘irregular’ – Get clock from external pin, and we are only interested in the number of occurrence of this pulse. This is called counter (counting events)ECE473/573Microprocessor System Design, Dr. Shiue 4Timer 0 and Timer 1• Two 16-bit timers: Timer 0 and Timer 1• Timer 0 (16-bit)• Timer 1 (16-bit)TH0 TL0TH1 TL1ECE473/573Microprocessor System Design, Dr. Shiue 5Setup the Timer and Counter• 2 registers: TMOD and TCON• TMOD: Timer Mode Register  Set the various timer operation mode.– TMOD is an 8-bit register where the lower 4 bits are set aside for timer 0 and the upper 4 bits are set aside for timer 1. MSBLSBGATE C/!T M1 M0 GATE C/!T M1 M0Timer 1 Timer 0ECE473/573Microprocessor System Design, Dr. Shiue 6TMOD RegisterGATE C/!T M1 M0• GATE: To start and stop the timer– GATE=1  HW control : is enabled only while INTx pin is ‘1’and TRx control pin (in TCON) is set. – GATE=0  SW control (used frequently) !INT1!INT0P3.3P3.2ECE473/573Microprocessor System Design, Dr. Shiue 7TMOD Register• C/!T: Timer or counter selection–C/!T = 0  Timer (input from internal system clock)the Osc. Crystal (1/12) is used to trigger the timer.–C/!T = 1  Counter (input from Tx input pin)• M1 and M0: Mode selection for timer and counterMode M1 M0000 13-bit timer/counter mode1 0 1  16-bit timer/counter mode21 0 8-bit auto reload timer/counter mode311 split timer/counter modeT1T0P3.5P3.4ECE473/573Microprocessor System Design, Dr. Shiue 8TCON RegisterMSBLSBTF1TR1 TF0 TR0 IE1 IT1 IE0 IT0Timer 1Timer 1Timer 0 Timer 0• TF1: Timer 1 overflow flag – TF1=1: Timer/counter 1 overflows.– TF1=0: processor vectors to the interrupt services.• TR1: Timer 1 run control bit –TR1=1: turn Timer 1 ON–TR1=0: turn Timer 1 OFFECE473/573Microprocessor System Design, Dr. Shiue 9TCON RegisterMSBLSBTF1 TR1 TF0 TR0 IE1IT1 IE0 IT0Timer 1Timer 1Timer 0 Timer 0• IE1: External interrupt 1 edge flag– IE1=1: external interrupt is detected.– IE1=0: when interrupt is processed. • IT1: Interrupt 1 type control bit – IT1=1: falling edge.– IT1=0: low level triggered external interrupt.ECE473/573Microprocessor System Design, Dr. Shiue 10Run Timer (SW Control)MSBLSBTR1 TR0Timer 1Timer 1Timer 0 Timer 0• Gate=0, SETB TR1  Run Timer 1SETB TR0  Run Timer 0• Gate=0, CLR TR1  OFF Timer 1CLR TR0  OFF Timer 0MSBLSBGATE=0 GATE=0Timer 1 Timer 0TMODTCONECE473/573Microprocessor System Design, Dr. Shiue 11Timer and Counter• Q2: Indicate which timer and which mode are selected for each of the following (a) MOV TMOD, #01H, (b) MOV TMOD, #20H, and (c) MOV TMOD, #12H.• Q3: Find the timers’ clock frequency and its period for various 8051-based systems with the following crystal frequencies. (a) 12MHz, (b) 16MHz, and (c) 11.0592MHz. • Q4: Find the value for TMOD if we want to program Timer 0 in mode 2, use 8051 XTAL for the clock source, and use instructions to start and stop the timer.ECE473/573Microprocessor System Design, Dr. Shiue 12Timer Mode 1 Program• Mode 1: 16-bit timer operation• Steps – 0000 ~ FFFFH to be loaded into the timers’ registers TH and TL. – Start timer: SETB TR0 (i.e. Run Timer 0) – Timer overflow flag (TF1 or TF0) should be monitored– Stop timer: CLR TR0 (OFF Timer 0)– Repeat: TH and TL are loaded again– TF reset to 000000001:FFFF0000OVECE473/573Microprocessor System Design, Dr. Shiue 13Steps to Program for Timer 0, Mode 1 Example• Steps: 1. Load the TMOD value (eg. MOV TMOD, #21H)2. Load TH0 and TL0 (eg. MOV TL0, #9CH & MOV TH0, 0FFH) 3. Start the timer (SETB TR0)4. Keep monitor the timer flag (TF0)target: JNB TF0, target  Jump out only if TF0=15. Stop the timer 0 (CLR TR0)6. CLR TF07. Repeat Step 2.ECE473/573Microprocessor System Design, Dr. Shiue 14Timer Delay Calculation• For XTAL=11.0592MHz(FFFF-YYXX+1) *1.085µs(65535-NNNNN) *1.085µsTH TLHexdecimalORNNNNN is a decimal value derived from YYXXHECE473/573Microprocessor System Design, Dr. Shiue 15Examples• Q5: In the following, we are creating a square wave of 50% duty cycle (with equal portions high and low) on the P1.5 bit. Timer 0 is used to generate the time delay. MOV TMOD, #01Here: MOV TL0, #0F2HMOV TH0, 0FFHCPL P1.5ACALL DelaySJMP HereDelay: SETB TR0Again: JNB TF0, AgainCLR TR0CLR TF0RETECE473/573Microprocessor System Design, Dr. Shiue 16Examples• Q6: See the example in Q5, calculate the amount of time delay in the DELAY subroutine generated by the timer. Assume XTAL =11.0592MHz. • Q7: Find the delay generated by timer 0 in the following code (Do not include the overhead due to instructions). CLR P2.3MOV TMOD, #01Here: MOV TL0, #3EHMOV TH0, #0B8HSETB P2.3SETB TR0Again: JNB TF0, AgainCLR TR0CLR TF0CLR P2.3ECE473/573Microprocessor System Design, Dr. Shiue 17Examples• Q8: Modify TL and TH in Q7 to get the largest time delay possible. Find the delay in ms. (Do not include the overhead due to instructions)• Q9: examples in Q7 and Q8 did not reload TH and TL, since it was a single pulse. The following program generates a square wave on P1.5 continuously using Timer 1 for a time delay. Find the frequency of the square wave if XTAL=11.0592MHz. (Not include overhead due to instructions)ECE473/573Microprocessor System Design, Dr. Shiue 18Examples• Assume we know the amount of timer delay, then how to find the values for TL and TH• Q10: Assume the XTAL =11.0592MHz, what value do we need to load into the timers’ registers if we