Thanks,  that site is very helpful.

Wesley Moore wrote:

> I would suggest you visit the following page. It has truck loads of info
> related to LCD's as well as source for the various aspects of LCD control
> including the busy flag.
>
> http://www.iaehv.nl/users/pouweha/lcd2.htm
>
> ___________________________________________
> Wesley Moore
> RMIT - BEng/BApp.Sc. 1st Year
>
> wmoore@cs.rmit.edu.au
> http://wmoore.tsx.org/
>
> On Mon, 25 Oct 1999, John Considine wrote:
>
> > I am having a problem when I try to check the busy flag coming from the
> > LCD display (BUSY_FLAG? subroutine shown below).  It is always busy but
> > if I remove the busy flag check it runs fine, as long as I use a slow
> > clock (therefore the display must not be busy).   Any suggestions why
> > this bit would be remaining high.   the power supply is a 7805 (5+)
> > being supplied by a 1 amp 12v power supply (120V wall plug in).  I have
> > a .1uf capacitor from +5 to ground and a .57uf cap from 12V to ground
> > (for decoupling so I think).  All of this is on a breadboard along with
> > the PIC 16C84 and Noritake LCD display 4X20 display with selectable 4 or
> > 8 bit transfer.
> > Thanks.
> >
> > ;October 25, 1999
> > ;
> >
> >
> >  LIST P=16C84, F=INHX8M, R=DEC
> >  include <p16c84.inc>
> >    __CONFIG _CP_OFF & _WDT_OFF & _RC_OSC
> >
> > DISP_ON   EQU  b'00001101'
> > CLR_DISP  EQU  b'00000001'
> > ENTRY_INC  EQU  b'00000110'
> > MSD   EQU  H'0C'
> > LSD   EQU  H'0D'
> > TEMP   EQU  H'0E'
> > TEMP1   EQU  H'0F'
> > CHAR   EQU  H'10'
> > RESET_V   EQU  0
> > LCD_DELAY_SET  EQU  H'FF'
> > DD_RAM_ADD  EQU  H'80'
> > E   EQU  4  ; LCD Enable control line
> > RW   EQU  3  ; LCD Read/Write control line
> > RS   EQU  2
> > ;interupt routine varibles
> > INT_W  EQU  H'11'
> > INT_S  EQU  H'12'
> >
> >    org 0
> > RESET   goto    START
> >    org 4     ; RESET vector location
> >
> > Int
> >  movwf INT_W
> >  movf STATUS, 0
> >  movwf  INT_S
> >
> > START
> > ;pic 16c84 setup for initial state
> >  movlw b'00000000'
> >  movwf STATUS   ;Clear Status
> >  clrf INTCON   ;Initialize INTCON Disable all interupts
> > ; bsf INTCON, 3  ;Makes interupt if RB<7:4> change state
> >  bsf STATUS,RP0
> >  movlw b'11000111'
> >  movwf OPTION_REG  ;Set Option Register
> >  bcf STATUS,RP0
> >
> >  clrf PORTA
> >  clrf PORTB
> >  bsf STATUS,RP0
> >  CLRF TRISA
> >  CLRF TRISB
> >  bcf STATUS,RP0
> >
> > ;display initialize
> >
> >  movlw H'20'   ;four bit transfer =h'20' 8 = h'38'
> >  movwf PORTB
> >  bsf PORTA,E
> >  bcf PORTA,E
> >
> >  movlw DISP_ON
> >
> >  nop
> >  nop
> >  nop
> >  nop
> >  nop
> >  movwf PORTB
> >  call CMD_SEND
> >
> > ; movlw CLR_DISP
> > ; call CMD_SEND
> >
> > ;send characters
> >  movlw 'F'
> >  call CHAR_REC
> >  movlw 'I'
> >  call CHAR_REC
> >  movlw 'N'
> >  call CHAR_REC
> >  movlw 'A'
> >  call CHAR_REC
> >  movlw 'L'
> >  call CHAR_REC
> >
> >  goto $
> >
> >
> >
> > CMD_SEND
> >   movwf   CHAR            ; Command to be sent is in W
> >        call    BUSY_FLAG?      ; Wait for LCD to be ready
> >         movf    CHAR, 0
> >        movwf   PORTB         ; Send data to LCD
> >         bcf     PORTA, RW  ; Set LCD in read mode
> >         bcf     PORTA, RS ; Set LCD in command mode
> >         bsf     PORTA, E      ; toggle E for LCD
> >         bcf     PORTA, E
> >     ;send lower nibble
> >  swapf CHAR, 0
> >  movwf   PORTB
> >  bsf PORTA, E
> >  bcf PORTA, E
> >         RETURN
> >
> > CHAR_REC
> >   movwf   CHAR            ; Command to be sent is in W
> >        call    BUSY_FLAG?      ; Wait for LCD to be ready
> >         movf    CHAR, 0
> >        movwf   PORTB         ; Send data to LCD
> >         bcf     PORTA, RW  ; Set LCD in read mode
> >         bsf     PORTA, RS ; Set LCD in command mode
> >         bsf     PORTA, E      ; toggle E for LCD
> >         bcf     PORTA, E
> >     ;low nibble transfer
> >  swapf CHAR,0
> >  movwf PORTB
> >  bsf PORTA, E
> >  bcf PORTA, E
> >         RETURN
> > ;
> > BUSY_FLAG?
> >
> >   bsf     STATUS,RP0       ; Select Register page 1
> >         movlw   0xF0             ; Set port_B for input
> >         movwf   TRISB
> >         bcf     STATUS, RP0      ; Select Register page 0
> >         bcf     PORTA, RS     ; Set LCD for command mode
> >         bsf     PORTA, RW    ; Setup to read busy flag
> >         bsf     PORTA, E      ; Set E high
> >         bcf     PORTA, E      ; Set E low
> >         movf    PORTB, 0      ; Read busy flag, DDram address
> >  andlw 0xF0
> >  movwf TEMP
> >  bsf PORTA, E
> >  bcf PORTA, E
> >  swapf PORTB, 0
> >  andlw 0x0F
> >  iorwf TEMP
> >  btfsc TEMP,7
> > ; goto BUSY_FLAG?
> >  nop
> >  bsf STATUS, RP0
> >  movlw 0x00
> >  movwf TRISB
> >  bcf STATUS, RP0
> >  RETURN
> >
> > ; movwf
> > ;       movwf   TEMP
> > ;        btfsc   TEMP, 7
> > ;           ; Check busy flag, high=busy
> > ;        goto    BUSY_FLAG?
> > ;        bcf     PORTA, RW
> > ;        bsf     STATUS, RP0      ; Select Register page 1
> > ;        movlw   H'00'
> > ;        movwf   TRISB      ; Set port_B for output
> > ;        bcf     STATUS, RP0      ; Select Register page 0
> > ;        RETURN
> >
> >  end
> >