I have been working on a project for school. It involves PIC assembly programming. I use 44 pin demo board, PIC16F887.
I have to do an IR receiver which has a output that changes a LED brightness. I know so far I have to make a PWM control for that. However I am still struggling with decoding the buttons. I am using an emitter that has NEC coding. My input setup is digital, pulled up with internal resistor PORTB, 0. I am trying to polling the input with TMR0 interrupts.
System setup is 4MHz oscillator, TMR0 is incrementing every Osc/4. Prescaler is 1:2, So every 2μs the timer is incrementing 1. Timer0 preload is D’206’, so it is interrupting 50*2μs = 100μs. According to the NEC protocol Logic 0 has 562,5μs low, Logic 1 has 1687,5μs low signal, after a 562,5 HIGH signal.
So 1687.5μs /100μs = 16, and 562.5μs / 100 μs = 5. I was trying to subtract them out of 8. So I can check what does STATUS, ZERO bit is active or low.
I don’t know in which part I am going wrong. I will leave my code down below. This code has a LED blinking, while it supposed to set PORTD,0 LED on if volume+ button is pressed. So in this way I would know if I can detect the buttons, and work on the PWM.
Every answer is appreciated.
ISR: ;IF ISR GLOBAL INT 0
btfss INTCON,T0IF
retfie ;if there is no interrupt
banksel 0 ;ISR occur in Bank0
movwf W_save ;save WORK register's value
movf STATUS,W
movwf STATUS_save ;save STATUS register's value
call IR ;call IR
goto ISR_EXIT
ISR_EXIT:
bcf INTCON,T0IF ;TMR0 interrupt flag clear
movlw b'01100110' ;preload 206
movwf TMR0
movf STATUS_save,W
movwf STATUS ;STATUS register original value reload
swapf W_save,f ;WORK register original value reload
swapf W_save,W
retfie ;retfie -> global int = 1
IR:
btfss PORTB,0 ;testing IR input
bsf ir_reg,0 ;button was pressed
btfss ir_reg,0 ;button was pressed?
goto NO_BUTTON
btfsc PORTB,0 ;HIGH signal?
goto HIGH_P
btfss ir_reg,1 ;previous was HIGH?
goto HIGH_TO_LOW
incf time,f ;increment time
goto ISR_EXIT
HIGH_P:
btfsc ir_reg,1 ;was previous LOW?
goto LOW_TO_HIGH
incf time,f ;increment time
goto ISR_EXIT
HIGH_TO_LOW: ;transition between HIGH to LOW pulses
bsf PORTD,3
movf time,W
movwf high_pulse ;saving HIGH pulse's time
clrf time ;time variable clear
bcf ir_reg,1 ;previous pulse was HIGH
goto CALC
CALC:
movf high_pulse,W ;high pulse's time into Work
bcf STATUS,Z ;STATUS ZERO CLEAR
sublw D'10' ;LOW_P -> 5-10 = -5,HIGH_P - > 16-10 = 6
btfsc STATUS,Z ;if subtraction = +
bsf ir_reg,3 ;subtraction ended positive -> LOGIC 1
bcf ir_reg,3 ;subtraction ended negative -> LOGIC 0
goto ADD_BITS
ADD_BITS:
bsf PORTD,2
btfsc ir_reg,3 ;if LOGIC 1
bsf STATUS,C ;carry bit 1
bcf STATUS,C ;carry bit 0
goto ROTATE
ROTATE:
bsf PORTD,1
rlf naddress ;Carry is rotated to naddress LSB
rlf address ;naddress MSB rotated to address LSB through Carry
rlf ncommand ;address MSB rotated to ncommand LSB through Carry
rlf command ;ncommand MSB rotated to command LSB through Carry
incf pulses ;every time we have a rotation increment variable
movf pulses,W
bcf STATUS,Z ;status zero clear
sublw D'32' ;33-pulses,we have a decoded signal
btfss STATUS,Z ;if Zero set
goto ISR_EXIT ;goto NO_button
goto LED_FLASH
LED_FLASH:
movf command,W
bcf STATUS,Z
sublw b'10101000' ;+ button command: b'10101000'
btfss STATUS,Z
goto NO_BUTTON
bsf PORTD,0
goto ISR_EXIT
LOW_TO_HIGH: ;transition between LOW to HIGH pulses
movf time,W
movwf low_pulse ;saving LOW pulse's time
clrf time ;time variable clear
bsf ir_reg,1 ;previous pulse was LOW
goto ISR_EXIT
NO_BUTTON:
btfsc PORTB,0
goto ISR_EXIT
clrf pulses ;clearing variables
clrf ir_reg
clrf time
clrf address
clrf naddress
clrf address
clrf ncommand
clrf command
goto ISR_EXIT
INIT:
;OSCCON INIT
banksel OSCCON
movlw b'01100000' ;4Mhz oscillator
movwf OSCCON
;OUTPUT INIT
banksel TRISD
clrf TRISD ;TRISD OUTPUT
banksel PORTD
clrf PORTD ;PORTD LOW
;INPUT INIT
banksel TRISB
bsf TRISB,RB0 ;RB0 INPUT
bsf WPUB,RB0
movlw 0x00
banksel ANSELH
movwf ANSELH ;RB0 DIGITAL
call Delay
;OPTION REG INIT / TMR0
banksel OPTION_REG
movlw b'00000000' ;TMR0 prescale 1:2 increment every 2us
movwf OPTION_REG
movlw b'01100110' ;preload 206
movwf TMR0 ;50 tick until overflow 50*2us = 100us
;INTCON INIT
banksel INTCON
bcf INTCON,T0IF ;TMR0 overflow flag clear
bsf INTCON,T0IE ;TMR0 overflow enable
bsf INTCON,GIE ;global interrupt enable
return
MAIN:
call INIT
call FLASH ;LED FLASH
goto $-1
END
In my arrogance I thought that your assignment was simple and straightforward.
I could not have been more wrong. It has taken me three days to code and test an application that can decode the NEC Infrared Remote control protocol.
There are significant challenges just trying to understand the alleged documentation found in various web sites. All of it is misleading and incomplete. It consumed a full day just sorting through that mess.
This is what I got working:
list n=0,c=255,r=dec ; Make .LST file look nice
errorlevel -302 ; Suppress Register in operand not in bank 0 warning.
#define MAIN_ASM
;
; File: main.asm
; Date: 2020-05-23
; Target: PIC16F887
; Author: dan1138
;
; Description:
; Decoder for NEC Infrared Remote control protocol.
;
; Physical transport:
; Long flash (> 8ms)
; Pause (COMMAND when pause is more than 4ms),
; (REPEAT when pause is less than 4ms but greater than 2ms)
; Short flash (0.5 to 0.6ms)
; Repeats 32 times:
; Pause DATA is one when pause is more than 1ms, else DATA is zero.
; Short flash (0.5 to 0.6ms)
;
;
; PIC16F887
; +----------:_:----------+
; VPP -> 1 : RE3/MCLR/VPP PGD/RB7 : 40 <> PGD
; <> 2 : RA0/AN0 PGC/RB6 : 39 <> PGC
; <> 3 : RA1/AN1 AN13/RB5 : 38 <>
; <> 4 : RA2/AN2 AN11/RB4 : 37 <>
; <> 5 : RA3/AN3 PGM/AN9/RB3 : 36 <>
; <> 6 : RA4/T0CKI AN8/RB2 : 35 <>
; <> 7 : RA5/AN4 AN10/RB1 : 34 <>
; <> 8 : RE0/AN5 INT/AN12/RB0 : 33 <> IR_RECEIVERn
; <> 9 : RE1/AN6 VDD : 32 <- 5v0
; <> 10 : RE2/AN7 VSS : 31 <- GND
; PWR -> 11 : VDD RD7 : 30 -> LCD_ON
; GND -> 12 : VSS RD6 : 29 -> LCD_E
; -> 13 : RA7/OSC1 RD5 : 28 -> LCD_RW
; <- 14 : RA6/OSC2 RD4 : 27 -> LCD_RS
; <> 15 : RC0/SOSCO RX/DT/RC7 : 26 <>
; <> 16 : RC1/SOSCI TX/CK/RC6 : 25 <>
; <> 17 : RC2/CCP1 RC5 : 24 <>
; <> 18 : RC3/SCL SDA/RC4 : 23 <>
; LCD_D4 <> 19 : RD0 RD3 : 22 <> LCD_D7
; LCD_D5 <> 20 : RD1 RD2 : 21 <> LCD_D6
; +-----------------------:
; DIP-40
;
; Include Special Function Register definitions
;
#include "p16f887.inc"
#include "main.inc"
#include "lcd.inc"
;
; PIC16F887 Configuration Bit Settings
; Assembly source line config statements
;
__CONFIG _CONFIG1, _FOSC_INTRC_NOCLKOUT & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _IESO_ON & _FCMEN_OFF & _LVP_OFF
__CONFIG _CONFIG2, _BOR4V_BOR21V & _WRT_OFF
;
; Power on reset vector
;
RES_VECT CODE 0x0000 ; processor reset vector
pagesel START
GOTO START ; go to beginning of program
;
; Interrupt context save area
;
ISR_DATA UDATA_SHR
WREG_SAVE res 1
STATUS_SAVE res 1
PCLATH_SAVE res 1
NEC_IR_State res 1
NEC_IR_StartFlash res 1
NEC_IR_CdPause res 1
;
; Data area for protocol decoder
;
NEC_IR_DATA UDATA
NEC_IR_RawData res 4
NEC_IR_Address res 1
NEC_IR_Command res 1
NEC_IR_Flags res 1
#define BIT_NEC_IR_Flags_COMMAND NEC_IR_Flags,0
#define BIT_NEC_IR_Flags_REPEAT NEC_IR_Flags,1
;
; Interrupt Service Routine
;
ISR_VECT CODE 0x0004 ; interrgot vector
ISR:
movwf WREG_SAVE ;
movf STATUS,W ; These register: WREG, STATUS, PCLATH
movwf STATUS_SAVE ; are what, at the minimum, must be saved
movf PCLATH,W ; and restored on an interrupt.
movwf PCLATH_SAVE ;
clrf STATUS ; Force to memory bank 0
clrf PCLATH ; Force to code page 0
;
; Handle external INT interrupt request
;
btfsc INTCON,INTE
btfss INTCON,INTF
goto INT_End
bcf INTCON,INTF
;
; Block flash detection until application loop is done
;
btfss BIT_NEC_IR_Flags_COMMAND
btfsc BIT_NEC_IR_Flags_REPEAT
goto INT_End
movf NEC_IR_State,F
skpz
goto NEC_IR_NextState
;
; Look for initial long flash
;
clrf NEC_IR_StartFlash
clrf TMR0
bcf INTCON,T0IF
MeasureStartFlash:
btfsc PORTB,0 ; Skip if flash still on
goto EndOfFlash
btfss INTCON,T0IF
goto MeasureStartFlash
bcf INTCON,T0IF
incfsz NEC_IR_StartFlash,W
movwf NEC_IR_StartFlash
goto MeasureStartFlash
EndOfFlash:
clrf TMR0
bcf INTCON,T0IF
clrf NEC_IR_CdPause
movlw 8
subwf NEC_IR_StartFlash,W
btfss STATUS,C ; Skip if count equal or greater than 8 T0IF ticks
goto INT_End
;
; Measure pause after flash
;
MeasurePause:
btfss PORTB,0 ; Skip if flash still off
goto EndOfPause
btfss INTCON,T0IF
goto MeasurePause
bcf INTCON,T0IF
incfsz NEC_IR_CdPause,W
movwf NEC_IR_CdPause
goto MeasurePause
EndOfPause:
btfss PORTB,0 ; Skip when flash goes off
goto EndOfPause
clrf TMR0
bcf INTCON,T0IF
bcf INTCON,INTF
movlw 4
subwf NEC_IR_CdPause,W
btfsc STATUS,C ; Skip if count less than 4 T0IF ticks
goto ReceiveCommandState
banksel NEC_IR_Flags
bsf BIT_NEC_IR_Flags_REPEAT ; Assert this is a REPEAT event
goto INT_End
ReceiveCommandState:
movlw d'32'
movwf NEC_IR_State ; Advnace to state 32 when we expect ADDRESS/COMMAND data
INT_End:
;
movf PCLATH_SAVE,W ;
movwf PCLATH ; Restore the saved context of the
movf STATUS_SAVE,W ; interrupted execution.
movwf STATUS ;
swapf WREG_SAVE,F ;
swapf WREG_SAVE,W ;
retfie ; Exit ISR and enable the interrupts.
;
; Receive COMMAND or REPEAT event
;
NEC_IR_NextState:
banksel PORTB
bcf STATUS,C
btfsc INTCON,T0IF
bsf STATUS,C
banksel NEC_IR_RawData
rlf NEC_IR_RawData,F
rlf NEC_IR_RawData+1,F
rlf NEC_IR_RawData+2,F
rlf NEC_IR_RawData+3,F
EndOfBit:
banksel PORTB
btfss PORTB,0 ; Skip when flash goes off
goto EndOfBit
clrf TMR0
bcf INTCON,T0IF
decf NEC_IR_State,F
btfss STATUS,Z
goto INT_End
;
; Validate ADDRESS and COMMAND
;
banksel NEC_IR_RawData
comf NEC_IR_RawData,W
xorwf NEC_IR_RawData+1,W
btfss STATUS,Z
goto INT_End
comf NEC_IR_RawData+2,W
xorwf NEC_IR_RawData+3,W
btfss STATUS,Z
goto INT_End
movf NEC_IR_RawData+1,W
movwf NEC_IR_Command
movf NEC_IR_RawData+3,W
movwf NEC_IR_Address
bsf BIT_NEC_IR_Flags_COMMAND
goto INT_End
;
; Initialize the PIC hardware
;
START:
clrf INTCON ; Disable all interrupt sources
banksel BANK1
clrf PIE1
clrf PIE2
movlw b'01100000'
movwf OSCCON ; Set internal oscillator at 4MHz
movlw b'10000001' ; Pull-ups off, INT edge high to low, WDT prescale 1:1
movwf OPTION_REG ; TMR0 clock edge low to high, TMR0 clock = FCY, TMR0 prescale 1:4
; TIMER0 will assert the overflow flag every 256*4 (1024)
; instruction cycles, with a 4MHz oscilator this ia 1.024 milliseconds.
movlw b'11111111' ;
movwf TRISA
movlw b'11111111' ;
movwf TRISB
movlw b'11111111' ;
movwf TRISC
movlw b'11111111' ;
movwf TRISD
; Set all ADC inputs for digital I/O
banksel BANK3
movlw b'00000000'
movwf ANSEL
movlw b'00000000'
movwf ANSELH
banksel BANK2
clrf CM1CON0 ; turn off comparator
clrf CM2CON0 ; turn off comparator
banksel BANK1
movlw b'00000000'
movwf ADCON1
clrf VRCON ; turn off voltage reference
banksel BANK0
movlw b'10000000'
movwf ADCON0
pagesel main
goto main
;
; Main data
;
MAIN_DATA UDATA
RepeatCount res 1
;
; Main application code
;
MAIN_PROG CODE
;
; Main application initialization
;
main:
lcall OpenXLCD
movlw LINE_ONE
lcall SetDDRamAddr
movlw LOW(LCD_message1)
movwf pszLCD_RomStr
movlw HIGH(LCD_message1)
movwf pszLCD_RomStr+1
lcall putrsXLCD
banksel NEC_IR_Flags
clrf NEC_IR_Flags
clrf NEC_IR_State
bcf BIT_NEC_IR_Flags_COMMAND
bcf BIT_NEC_IR_Flags_REPEAT
bcf INTCON,INTF
bsf INTCON,INTE
bsf INTCON,GIE
;
; Application process loop
;
AppLoop:
movf NEC_IR_Flags,F ; Check for event
btfsc STATUS,Z ; Skip if any event bit set
GOTO AppLoop ;
banksel NEC_IR_Flags
btfsc BIT_NEC_IR_Flags_REPEAT ; skip of not a REPEAT event
goto IncrementCount
banksel RepeatCount
clrf RepeatCount
;
; Increment repeat count
;
IncrementCount:
banksel RepeatCount
incfsz RepeatCount,W
movwf RepeatCount
;
; Show measurement for Start Of Transmission (SOT) flash
;
movlw LINE_TWO
lcall SetDDRamAddr
movf NEC_IR_StartFlash,W
lcall PutDecXLCD
;
; Show measurement for pause after SOT flash
;
movlw ' '
lcall WriteDataXLCD
movf NEC_IR_CdPause,W
lcall PutDecXLCD
;
; Show decoded ADDRESS and COMMAND
;
movlw ' '
lcall WriteDataXLCD
banksel NEC_IR_Address
movf NEC_IR_Address,W
lcall PutHexXLCD
banksel NEC_IR_Command
movf NEC_IR_Command,W
lcall PutHexXLCD
;
; Show REPEAT count
;
movlw ' '
lcall WriteDataXLCD
banksel RepeatCount
movf RepeatCount,W
lcall PutHexXLCD
;
; Clear event flags to enable capture of next event
;
banksel NEC_IR_Flags
clrf NEC_IR_Flags
lgoto AppLoop
;
; LCD messages
;
MAIN_CONST code
LCD_message1:
dt "NEC IR Decode v0",0
END
I have written a lot of code in assembly language for 8-bit PIC controllers. This application is dense with some very subtle tricks. There are not enough comments in it to explain how and why it works. You are just going to have to analyze it for yourself.
The trick with the NEC IR protocol is that it's all about the pauses between the flashes of IR. If there is an accurate, complete and understandable description of the NEC IR control protocol on the Internet I could not find it.
I was thinking it would be possible to teach you how to code this but I do not think I am good enough to pull that off. I can only hope this can work as an example for you.