PIC16 MCU Peripherals-Computer Archtecture-Lecture Slides, Slides of Computer Architecture and Organization

Download PIC16 MCU Peripherals-Computer Archtecture-Lecture Slides and more Slides Computer Architecture and Organization in PDF only on Docsity!

PIC16 MCU Peripherals

• Digital I/O• Timers• A/D converter• Comparator• Parallel slave port• Interrupts

PIC 16F877 Timers/Counters

• Three hardware timers built in:
  • Timer0 (originally called RTCC, the real-time

counter clock)

• Timer1– Timer

Programming Timers

• Clock Sources
  • Internal Clock Makes it a Timer– External Clock Makes it a Counter
    • Basic Registers
      • TMRxL – Timer/Counter Register Low– TMRxH – Timer/Counter Register High– TCON – Timer Control Register– INTCON – Interrupt Control Register

CCS timer functions

• The number of bits in the timer (8 or 16)

determines the maximum count (256 or65536, respectively).

• When the timer register overflows and

returns to zero, an overflow flag bit is set.

• This flag can be polled (tested) to check if

an overflow has occurred or an interruptgenerated, to trigger the required action.

•^

To modify the count period, the timerregister can be preloaded with a givennumber.

• For example, if an 8-bit register is

preloaded with the value 156, a time-outoccurs after 256 – 156 = 100 clocks.

• Many timer modules allow automatic

preloading each time it is restarted,

• For example, the 8-bit timer driven at 1

MHz with a prescale value of 4 counts upto 256 x 4 =

μ

s, at 4

μ

s per bit.

• A postscaler has a similar effect,

connected at the output of the counter.

Counter Operation

• A counter/timer register consists of a set of

bistable stages (flip-flops) connected incascade (8, 16, or 32 bits).

• When used as a counter, a pulse train fed

to its least significant bit (LSB) causes theoutput of that stage to toggle at half theinput frequency.

Timer Operation in 16F

• The count can be recorded at any chosen

point in time; alternatively,

• an interrupt can be generated on overflow

to notify the processor that the maximumcount has been exceeded.

• If the register is preloaded with a suitable

value, the interrupt occurs after a knowncount.

• The counters are more frequently used as

timers, with the input derived from theMCU clock oscillator.

• Since the clock period is accurately

known, the count represents an accuratetimed period.

• It can therefore be used to measure the

period or frequency of an input signal orinternal intervals or generate a regularinterrupt.

General Timer Operation

Binary Counter

Pre-scaler(clockdivide)

Post-scaler(outputdivide)

TimerOverflow/Timeout(Interrupt)Flag

ClockSourceSelect

InstructionClockExternal Pulse

Captureregister Compareregister

Capturesignal

Match flag

A binary counter is used as a timer when driven from the clock

Timer 0

• Timer0 is an 8-bit

register that can countpulses at RA4; for thispurpose, the input iscalled T0CKI (Timer0clock input).

• Timer0 has a

prescaler that dividesby up to 128;

Timer 2

• Timer2 has a prescaler and postscaler that

divide by up to 16.

Assignment

• Generate a Pulse of 1 Hz at one output

and show it on an LED

• Count the number of times key is pressed

by your friend.