Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

;|

;|_____ * indicates setup values presently selected

;========================= ; setup and configuration ;=========================

;============================================================

; M A C R O S

;============================================================ ; Macros to select the register banks

;=====================================================

; constant definitions for pin wiring

;=====================================================

;=====================================================

; PIC register and flag equates

;=====================================================

;======================================================

; variables in PIC RAM

;=====================================================

;=========================================================

; program

;=========================================================

main:

Bank1

; Port-A bits 0 and 2 are input. All others are output

;Prepare to set prescaler clrf TMR0 clrwdt

;Setup OPTION register for full timer speed

;|__________________________ RBPU pullups

;=========================

;wait for READY switch

;to be pressed ;=========================

;data received ;===========================

;Turn ready to receive LED off

;============================================================

;============================================================

;ON ENTRY:

;local variable dataReg is used to store 8-bit value

;received through port (labeled serialLN)

;OPERATION:

;1. The timer at register TMR0 is set to run at

;maximum clock speed, that is, 256 clock beats.

;The timer overflow flag in the INTCON register

;is set when the timer cycles from 0xff to 0x00.

;2. When the START signal is received, the code

;waits for 128 timer beats so as to read data in

;the middle of the send period.

;3. Each bit (start, data, and stop bits) is read

;at intervals of 256 timer beats.

;4. The procedure tests the timer overflow flag

;(tmrOVF) to determine when the timer cycle has

;ended, that is when 256 clock beats have passed.

;=============================================================

rcvData:

;=========================

; wait for START bit

;=========================

;=========================

;offset 128 clock beats ;=========================

;At this point the receiver has found the falling

;edge of the start bit. It must now wait 128 timer

;beats to synchronize in the middle of the sender’s

;data rate, as follows:

;======================== return

;========================================================= ; end of program ;=========================================================

end

14.5.3 Serial6465 Program

;File name: Serial6465.asm

;Last update: May 7, 2006

;Author: Julio Sanchez

;Processor: 16F84A

;Description:

;Program to exercise serial communications using a

;PIC 16F84A and two shift registers: a 74HC164, and a

;74HC165. The 74HC165 inputs 8 lines from a DIP switch

;and transmits settings to PIC through a serial line.

;PIC sends data serially to an 74HC164 which is wired

;to 8 LEDs that display the received data. A total of

;6 PIC lines are used in interfacing 8 input switches

;to 8 output LEDs.

;Circuit:

;* Port A0 is the serial transmission line which

;comes from the 74HC165.

;* Port A1 is wired to the 74HC164 CLOCK pin

;* Port A2 is wired to the 74HC164 CLEAR pin

;* 74HC164 output pins 0 to 7 are wired to LEDs.

;* Port B0 is wired to the 74HC165 Hout line

;* Port B1 is wired to the 74HC165 CLK line

;* Port B2 is wired to the 74HC165 load line

;* A pushbutton switch is in the 16F84 RESET line

;and serves to restart the program

;Communications protocol:

;Communication between PIC and the 74HC164 and

;74HC165 is synchronous since the shift registers

;clock lines serve to shift in and out the data

;bits.

;

;===========================

;switches ;===========================

;Switches used in __config directive: