;-------------------------------------------------------------------------; ; WORKTIME.ASM Pushbutton toggles clock keeping track of time on LCD ; ;-------------------------------------------------------------------------; ; Note: must add additional time digit to run over 99 hrs. LIST P=16F84 ; 16F84 Runs at 4 MHz INCLUDE "p16f84.inc" __CONFIG _PWRTE_ON & _LP_OSC & _WDT_OFF ; uses 32.768 kHz crystal ERRORLEVEL -224 ; supress annoying message because of tris ; Define Information #DEFINE RS PORTA, 0 #DEFINE E PORTA, 1 #DEFINE TOGGLESW PORTB, 4 ; Macro EStrobe MACRO ; Strobe the "E" Bit bsf E bcf E ENDM CBLOCK 0CH sec ; seconds digit sec10 ; 10's of second digit mins ; minutes digit min10 ; 10's of minutes digit hr ; hours digit hr10 ; 10's of hours digit highlim ; high limit + 1 of digit w_temp ; holds W during interrupt status_temp ; holds STATUS during interrupt fsr_temp ; holds FSR during interrupt Dlay ; 8 Bit Delay Variable working ; working flag 0 not working, 1 working ptr ; used in displaying message Temp ; a temporary variable bin ; a temporary variable oset ; offset of time register oldtime ; holds last value of sec ENDC ORG 0 ; start at location 0 goto main ; jump over to main routine ORG 4 goto isr ; jump to interrupt routine ;-------------------------------------------------------------------------; ; High limit + 1 of digits at position W ; ;-------------------------------------------------------------------------; sethi: addwf PCL, f dt H'A',H'6',H'A',H'6',H'A',H'A' ;-------------------------------------------------------------------------; ; Data for message to be output ; ;-------------------------------------------------------------------------; shomsg ; Message to Output addwf PCL, f ; Output the Characters dt "Working Time:", 0 ;-------------------------------------------------------------------------; ; Interrupt routine, increments time by one second (BCD) ; ;-------------------------------------------------------------------------; isr: movwf w_temp ; save W swapf STATUS,W ; save status movwf status_temp ; without changing flags swapf FSR,W ; save FSR movwf fsr_temp ; without changing flags movf working, f ; check working flag btfsc STATUS, Z ; if not zero then increment time goto restore ; else get out of interrupt routine movlw sec ; point at sec register movwf FSR newdigit: incf INDF, f ; current digit up one movlw sec ; get difference between sec and FSR subwf FSR, W call sethi ; use to get high limit + 1 subwf INDF, W ; reached that number yet? btfss STATUS, Z ; skip over if yes goto restore ; else exit isr clrf INDF ; set current digit to 0 incf FSR, f ; point at next digit goto newdigit ; no, increment the next digit restore: swapf status_temp,W ; get original status back movwf STATUS ; into status register swapf fsr_temp,W ; get original fsr back movwf FSR ; into status register swapf w_temp,f ; old no flags trick again swapf w_temp,W ; to restore W bcf INTCON,T0IF ; clear the TMR0 interrupt flag retfie ; finished reset GIE ;-------------------------------------------------------------------------; ; Initialize the ports ; ;-------------------------------------------------------------------------; init: clrf PORTA clrf PORTB movlw 0 ; Port A all outputs tris PORTA movlw B'00010000' ; RB4 input, others outputs tris PORTB movlw B'00000100' ; pull-ups enabled ; prescaler assigned to TMR0 ; prescaler set to 1:32 ; rolls over each second option movlw 0 ; zero out all registers movwf hr10 movwf hr movwf min10 movwf mins movwf sec10 movwf sec clrf working ; working flag to zero movlw B'10100000' ; GIE set T0IE set, T0IF cleared movwf INTCON return ;-------------------------------------------------------------------------; ; Initialize the LCD ; ;-------------------------------------------------------------------------; initlcd: movlw D'40' call nmsec ; Wait 40 msecs before Reset bcf RS ; send an 8 bit instruction movlw 0x03 ; Reset Command call NybbleOut ; Send the Nybble call Dlay5 ; Wait 5 msecs before Sending Again EStrobe nop nop ; Wait 244 usecs before Sending the Second Time EStrobe nop nop ; Wait 244 usecs before Sending the Third Time bcf RS ; send an 8 bit instruction movlw 0x02 ; Set 4 Bit Mode call NybbleOut nop nop movlw 0x028 ; 4 bit, 2 Line, 5x7 font call SendINS movlw 0x010 ; display shift off call SendINS movlw 0x001 ; Clear the Display RAM call SendINS call Dlay5 ; Note, Can take up to 4.1 msecs movlw 0x006 ; increment cursor call SendINS movlw 0x00C ; display on cursor off call SendINS return ;-------------------------------------------------------------------------; ; Send the character in W out to the LCD ; ;-------------------------------------------------------------------------; SendASCII addlw '0' ; Send nbr as ASCII character SendCHAR ; Send the Character to the LCD movwf Temp ; Save the Temporary Value swapf Temp, w ; Send the High Nybble bsf RS ; RS = 1 call NybbleOut movf Temp, w ; Send the Low Nybble bsf RS call NybbleOut return ;-------------------------------------------------------------------------; ; Send an instruction in W out to the LCD ; ;-------------------------------------------------------------------------; SendINS ; Send the Instruction to the LCD movwf Temp ; Save the Temporary Value swapf Temp, w ; Send the High Nybble bcf RS ; RS = 0 call NybbleOut movf Temp, w ; Send the Low Nybble bcf RS call NybbleOut return ;-------------------------------------------------------------------------; ; Send the nibble in W out to the LCD ; ;-------------------------------------------------------------------------; NybbleOut ; Send a Nybble to the LCD movwf PORTB EStrobe ; Strobe out the LCD Data nop nop return ;-------------------------------------------------------------------------; ; Output the message on the LCD ; ;-------------------------------------------------------------------------; OutMessage: movwf FSR ; Point at first letter OutLoop: movf FSR, w ; Get pointer into W incf FSR, f ; Set up for next letter call shomsg ; Get character to output iorlw 0 ; At the End of the Message? btfsc STATUS, Z ; Skip if not at end return ; Yes - Equal to Zero call SendCHAR ; Output the ASCII Character goto OutLoop ; Get the next character ;-------------------------------------------------------------------------; ; Wait until button is released ; ;-------------------------------------------------------------------------; waitup: btfss TOGGLESW ; test toggle switch goto $ -1 ; ck again if pressed movlw 20 ; wait 20 msec for debounce call nmsec btfss TOGGLESW ; check again, still up? goto $ -4 ; no start over return ; yes, finished ;-----------------------------------------------------------------------; ; Delay routine ; ;-----------------------------------------------------------------------; Dlay5 movlw 5 ; delay for 5 milliseconds nmsec: ; delay for # msec in W on entry nop ; each nop is 0.122 milliseconds nop nop ; each total loop is 8 X 0.122 = 0.976 msec nop addlw H'FF' ; same as subtracting 1 from W btfss STATUS, Z ; skip if result is zero goto nmsec ; this is 2 X 0.122 msec return ; back to calling point ;-------------------------------------------------------------------------; ; Display the Time ; ;-------------------------------------------------------------------------; DispTime MOVLW H'C0' CALL SendINS MOVF hr10, W CALL SendASCII MOVF hr, W CALL SendASCII MOVLW ":" CALL SendCHAR MOVF min10, W CALL SendASCII MOVF mins, W CALL SendASCII MOVLW ":" CALL SendCHAR MOVF sec10, W CALL SendASCII MOVF sec, W CALL SendASCII RETURN ;-------------------------------------------------------------------------; ; Toggle Work Flag ; ;-------------------------------------------------------------------------; togglewk: movf working, f ; set zero flag if zero btfss STATUS, Z ; skip if working is zero goto turnoff incf working, f ; set working to 1 call waitup ; wait for button release return turnoff: clrf working ; working set to zero call waitup ; wait for button to be released return ;-------------------------------------------------------------------------; ; The Main routine ; ;-------------------------------------------------------------------------; main: call init ; initialize ports, set up timer call initlcd ; initialize the LCD movlw 0 ; display 'Working Time:' call OutMessage ckbutton: ; check for a press of the TOGGLE button btfss TOGGLESW ; skip if not pressed call togglewk ; else change the mode of timer movf oldtime, W ; is oldtime the same as sec? subwf sec, W btfsc STATUS, Z ; if not, skip over next instruction goto ckbutton ; else continue checking call DispTime ; sec has changed, display the time movf sec, W ; make sec and oldsec the same movwf oldtime goto ckbutton ; and continue checking end
This program is a timer with pushbutton to start and stop accumulating time. The output is displayed on a Liquid Crystal Display, (LCD). An interrupt service routine, (isr), runs in the background. Every second it checks a flag called 'working'. The register 'sec' is incremented if the flag is set. An overflow of sec increments sec10 and so forth through tens of hours.
The display will flicker if the main loop displays the time continuously. Instead, the current seconds values is checked against the last displayed seconds value in 'oldtime'. Only if they are different is the display and oldtime updated.
Notice that there are two entry point to the subroutine that displays characters. At the entry point 'SendASCII', the value of the character '0' is added to W changing a binary number to an ASCII character. Sending instructions differs from sending characters. The RS line is high when sending characters, low for instructions.
Tables are used twice in this program. One table holds overflow values for each time register. The second holds the characters of a message to be displayed on the LCD. In both cases, the value of W on entry determines the value returned in W.
This is the first program to use a macro. The two instructions of the macro 'EStrobe' are inserted at each location in the program where the name of the macro, (EStrobe), appears. The puropose of the macro is to make the program easier to read.
Surplus LCD units that use the Hitachi 44870 controller can be purchased from B.G. Micro, (http://www.bgmicro.com), for as little as $3. Another supplier is Marlin P. Jones, (http://www.mpja.com). This program requires at least a two line by 16 character unit.
The first thing to do when you get your LCD is to confirm that it works. Apply +5 volts to pin 2 and ground pin 1. Also ground pin 3 which is the contrast voltage. You should see a line of squares where the characters appear. You may have to look at a low angle to see these. If you see nothing, the contrast voltage may not be right. Put a 10K, (or so), pot between +5 and ground and run the wiper to pin 3. Adjust the pot and see if you can make the squares appear and disappear. Some units require a negative contrast voltage.
We must go through a complex procedure just to initialize the display. We also put it into 4 bit mode so only six control 6 wires are needed instead of ten. If you want to read more about the 44780, here are some URL's:
The purpose of this program was to demonstrate a simple application that uses a LCD display. It does contain many elements you would use in any program with a LCD display unit. Among these are:
Try to use subroutines from this program to change some of the previous programs to use a LCD display as an output device.
Comments:
Dear Sir,+
Thank you for this rich website.
one comment: i selected a project(program 8) from the projects page and implemented the circuit.Unfortunately it dosent work (the LCD didnt display the timer), so what is the problem.
Thank you in advance.
Questions:
Christian Hultqvist Says: " how do i get this to work with 10mhz external reference clock/xtal " James Newton of Massmind replies: With great difficulty. The pre-scaler in the uC can't divide by a multiple of 10 (just 1/32, 1/64, 1/128, etc) so although you start with a nice 10Mhz clock, you end up with an ISR that runs every 10/32 or so on cycles. You might want to look at the page on timers.+
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