The Timer RB output pin P31 (TRB0) is connected to a point LED to view the mono shot pulse duration.

Transcription

1 Introduction: Generation of One shot pulse using Timer RB in Programmable one shot generation mode. To the timer output, an LED is connected and the pulse width is generated in terms of seconds, so that it is visible to the eyes. Hardware: To generate a one shot pulse, the internal peripheral Timer RB of the R8C micon is used. R8C has a range of Timers, Timer RA, Timer RB and Timer C. Each timer has different modes of operations. Timer RB is used in Programmable one shot generation mode. The Timer RB output pin P (TRB0) is connected to a point LED to view the mono shot pulse duration. To trigger the monoshot generation, a push button switch is connected to the INT0 input. When the input is triggered through the switch, the timer RB generates the mono shot pulse on the TRB0 pin.

2 Circuit: C NC PF XIN/P46 PF 9 XOUT/P47 C NC C NC C NC PROGRAM NORMAL EX U A A A A4 A5 A6 A7 A8 C8 0.uF Decoupling R4 0E 8 B B 7 R5 0E B 6 R6 0E B4 5 R9 0E B5 4 R0 0E B6 R 0E B7 R 0E B8 R 0E 74LS45 LED mm RED LED LED mm RED LED LED4 mm RED LED LED5 mm RED LED LED6 mm RED LED LED7 mm RED LED LED8 mm RED LED LED9 mm RED LED 9 G DIR 0 GND VCC 0 R 0K C C4 + U JP XTAL 0MHZ C5 PF XTAL.768KHZ C6 PF JP6 JP4 D IN448 U CD4006 C6 4.7uF 0K R6 SW 8 Push Button Switch JP JP5 6 P4/XCIN 7 P44/XCOUT R 4K7 5 MODE U 4 CD4006 JP P/TRDIOC0 P/TRDIOD0 P5/TRDIOB P6/TRDIOC P7/TRDIOD P0/TRAO P/TRBO P/SSI P4/SDA/SCS P5/SCL/SSCK P7/SSO 4 R8C 4/ VSS VCC 8 RESET P0/TRDIOA0/TCLK P/TRDIOB0 P4/TRDIOA P/KI/AN9 P/KI/AN0 P/KI/AN P4/TXD0 P5/RXD0 P6/CLK0 P7/TRAIO/INT P60/TREO P6 P6 P6 P64 P65/CLK P66/INT/TXD P67/INT/RXD P45/INT P00/AN7 P0/AN6 P0/AN5 P0/AN4 P04/AN P05/AN P06/AN P07/AN SW RESET 44 P4/VREF Note: Dotted lines indicate the required connections meant for the study. C 0.uF P0/KI0/AN8

3 Connections: LED Push Button Switch -> P (TRB0) -> P45 (INT0) Functional Description: Here, the two timers Timer RA and Timer RB are cascaded. Timer RB is used in one shot wave form generation mode and timer RA in timer mode. The clock for timer RB is coming from the underflow signal of Timer RA. Both the Timers operate in the down counter mode. Timer RA counts the internal clock and the clock frequency of fosc/8 is selected. Timer RB is operated in one shot generation mode to generate a one shot pulse. The clock for timer RB is obtained from the underflow signal of the Timer RA. Timer RA is operated in timer mode. The clock is divided by the Timer RA and generates a low frequency clock of 8Hz (approx.). Both the prescalar and the primary registers are loaded with 55. This low frequency signal coming out of timer RA becomes clock input to Timer RB. The division ratio is obtained as (Fosc / 8 ) = (n+) (m+) n - Prescaler value m - Primary register ( / 8) = (56)* (56) = 8 Hz ( approx.)

4 Timer RB again divides this clock using its prescalar register to Hz. The prescalar is loaded with 7. Hence the clock is divided by 8 to generate a Hz. Set a count of to Timer RB primary register TZPR to get a time delay of second. This will be the one shot pulse duration. One Shot Pulse Duration is (n+) (m+) = Timer RA underflow n - Prescalar value m - Primary register (8) * () = = Second ( approx.) The INT0 pin acts a trigger input pin for one shot pulse generation. When a trigger is given using the push button switch, the timer RB outputs a high level in its TRB0 pin for the predefined time (as initialized in timer RB) and then changes to low level. Here the one shot pulse time is set as second. Registers used: TRAPRE - 8-bit Prescalar RA Register TRA - 8-bit Timer RA Primary Register TRAMR - Timer RA Mode Register TRACR - 8-bit Timer RA Control Register TRBMR - Timer RB Mode Register TRBCR - 8-bit Timer RB Control Register TRBPRE - 8-bit Prescalar RB Register TRBPR - 8-bit Timer RB Primary Register TRBIOC - 8-bit Timer RB I/O Control Register 4

5 Timer RA Mode Register - TRAMR Load TRAMR register with H 0 to set timer RA in timer mode and clock is selected as Fosc/8. Timer RA Control Register - TRACR Set TSTART bit to level to start the timer RA. 5

6 Timer RB Mode Register - TRBMR Using Timer RB mode register, programmable one shot mode is set. Set TMOD0 to 0 and TXMOD bit to choose one shot mode. Set TZWC to. Set TCK0 to 0 and TCK to to select underflow of timer RA as clock to Timer RB. 6

7 Timer RB I/OControl Register - TRBIOC The Timer RB outputs a high level for one shot pulse and the corresponding trigger is enabled for INT0 pin by the following settings. Set TOPL to 0 level, set INOSTG to level. Timer RB Control Register - TRBIOC Set TSTART bit to level to start the timer RB. 7

8 Software Description: Initialize timer RA. Start the timer RA. Timer RA will generate clock for the Timer RB. Initialize Timer RB to operate in the one shot waveform generation mode with external trigger INT0 pin. When the trigger is received, the Timer RB will generate a high pulse through the TRB0 for seconds. After second the TRB0 line is lowered. Connect a LED to the TRB0 line, to view the one shot pulse width. The functions in the file Demo4.C and short descriptions are listed below: Functions Description main Main routine displays a message on LCD and does the initializations of Timers RA and RB MCUInitialize Initializes Micon InitializeTimerRARB Initializes Timers RA and RB 8

9 Program Flow: Start Initialize Micons main clock Turn off Ring Ocsillator Main clock = fosc Initialize Timer RA Set Timer Mode, fosc/8 Set Prescalar to 55 Set TRA to 55 Start Timer RA Initialize Timer RB Set One Shot mode Set Prescalar to 7 Set TRBPR to 5 Enable One shot triggger Enable INT0 bit Start Timer RB Halt Execute Demo: When a trigger pulse is given through INT0 line, the timer RB generates a one shot pulse in its output pin TRB0 for a period of Second (approx.). LED connected to TRB0 will be switched on for that time and will be switched off again. 9

10 Use Topview Simulator to Verify the Design. Open the project Demo4 in the R8C/Tiny System Simulator using Open Project option from Project menu. The project window opens up along with the Demo4.c file. Use Build option from Build menu to compile the project. An output window captures the compiler ouput. Use Project -> Download Project from main menu to download the.mot file into the simulator s memory for simulation. Connect point LED to the port line Pusing LED module setting and connect one push button switch to the port line P45 to give the trigger signal to timer RD using keyboard module setting. Open the LED and keyboard window and arrange them as shown for better visibility. 0

11 Down load the program using Download Project command in Project menu. Run the program using Go command in Run menu. Now the LED connected to the port line P will be in off state and timer RB is waiting for trigger signal from P45. Give the trigger signal to port line P45 by pressing the push button switch connected to P45 in keyboard window. The LED will now switched on to indicate that the output of the mono shot of timer RB is level. Ater 0 to 5 seconds the LED will be switched off according to the PC speed and other things. Because in Topview Simulator we cann t simulate the timings signals as per actual as in the real hardware.