Applications of Microcontroller-i prof. Ramakant Patil
NOTE 1: Note that even in capture mode, an overflow of Timer 2 will result in TF2 being set and an interrupt being triggered. NOTE 2
Download 1.23 Mb.
|
- Navigate this page:
- TIMER 2 INTERRUPT
- 3.2 PCA (Programmable Counter Array)
- PCA TIMER/COUNTER
NOTE 1: Note that even in capture mode, an overflow of Timer 2 will result in TF2 being set and an interrupt being triggered. NOTE 2: Capture mode is an efficient way to measure the time between events. At the moment that an event occurs, the current value of Timer 2 will be copied into RCAP2H/L. However, Timer 2 will not stop and an interrupt will be triggered. Thus your interrupt routine may copy the value of RCAP2H/L to a temporary holding variable without having to stop Timer 2. When another capture occurs, your interrupt can take the difference of the two values to determine the time transpired. Again, the main advantage is that you don't have to stop timer 2 to read its value, as is the case with timer 0 and timer 1. TIMER 2 INTERRUPT As is the case with the other two timers, timer 2 can be configured to trigger and interrupt. In fact, the text above indicates a number of situations that can trigger a timer 2 interrupt. To enable Timer 2 interrupt, set ET2 (IE.5). This bit of IE is only valid on an 8052. Similarly, the priority of Timer 2 interrupt can be configured using PT2 (IP.5). As always, be sure to also set EA(IE.7) when enabling any interrupt. Once Timer 2 interrupt has been enabled, a Timer 2 interrupt will be triggered whenever TF2 (T2CON.7) or EXF2 (T2CON.6) are set. The Timer 2 Interrupt routine must be placed at 002Bh in code memory. 3.2 PCA (Programmable Counter Array): PCA provides more timing capabilities with less CPU intervention than the standard timer/counter. Its advantages include reduced software overhead and improved accuracy. The PCA consists of a dedicated timer/counter which serves as the time base for an array of five compare/capture modules. Figure 3-1 shows a block diagram of the PCA. External events associated with modules are shared with corresponding Port 1 pins. Port pins not used by the PCA modules can still be used for standard I/O. Each of the five modules can be programmed in any of the following modes: • Rising and/or falling edge capture • High speed output • Watchdog Timer (Module 4 only) • Pulse Width Modulator (PWM)
The PCA timer is a free-running 16-bit timer consisting of registers CH and CL (the high and low bytes of the count values). The PCA timer is common time base for all five modules and can be programmed to run at 1/12 the oscillator frequency, 1/4 the oscillator frequency, Timer 0 overflow, or the input on the ECI pin (P1.2). The timer/counter source is determined from the CPS1 and CPS0 bits in the CMOD SFR as shown in Table 3-1. Table 3-2 summarizes Modes 0-3 clock inputs at two common frequencies. 
Directory: uploads uploads -> 587 Return function, r i(X) r i(0) r i(1) r i(2) r i(3) 1 0 2 4 6 Thermal Station, I 2 0 1 5 6 3 0 3 5 6 10 uploads -> Department of science and humanities department of mathematics part-a questions and answers uploads -> The Case Against the nypd’s Quota-Driven ‘Broken Windows’ Policing What Is It? uploads -> For want of a nail uploads -> Ownership Models There are two different types of ownership models uploads -> Police Militarization uploads -> City of rising star regular meting thursday, july 14, 2016 uploads -> Township of winfield uploads -> Stop Militarizing Law Enforcement Act of 2014 uploads -> The Black Panther Party’s Ten-Point Program What We Want Now! Download 1.23 Mb. Share with your friends:
|