Introduction to Microcontrollers Lab Manual - Microchip

1.1 OBJECTIVE
1.2 PRE-LAB
Lab 1. Timers
The lab covers the following concepts:
• PIC24F hardware timer modules
• Assembly language CALL and RCALL instructions
• Using MPLAB IDE to measure code execution time
1.2.1 Reference Material
• PIC24FJ256GB110 Family Data Sheet (DS39897)
• 16-Bit MCU and DSC Programmer’s Reference Manual (DS70157)
• MPLAB IDE User’s Guide (DS51519)
• PIC24F Reference Manual – Section 14. Timers (DS39704)
1.2.2 Timers
LABS
The PIC24FJ256GB110 device offers five (5) 16-bit timers/counters designated as
Timer1, Timer2, …
With certain exceptions, all of the 16-bit timers have the same functional circuitry. The
16-bit timers are classified into three types to account for their functional differences:
• Timer1 is a Type A timer
• Timer2 and Timer4 are Type B timers
• Timer3 and Timer5 are Type C timers
Type B and Type C timers can be combined to form a 32-bit timer.
Each timer module consists of the following readable/writable registers:
• TMRx: 16-bit Timer Count register
• PRx: 16-bit Timer Period register associated with the timer
• TxCON: 16-bit Timer Control register associated with the timer
Timers can be run from either an external clock connected to the TxCK pin, or the internal
clock (Fosc/2). This lab will use the internal clock as the MX PIC24F EDU Module
does not connect an external clock to the TxCLK pins.
1.2.3 Subroutine CALL
A subroutine CALL in assembly is a powerful tool for reusing code and keeping your
code clean and legible. Low-level functions can be abstracted into higher level functions
by the use of subroutine. This is similar to the use of a function in the 'C' language.
In fact, 'C' functions make use of the RCALL assembly instruction.
A CALL is similar to a GOTO or BRA instruction except that it stores the address of the
next instruction and allows you to return to it with the RETURN instruction.
2011 Microchip Technology Inc. DS51963A-page 13