;                           File Name C750DSP.ASM
;                   Single Message, Moving Message Display

; *************** USE METALINKS (( ASM51.EXE )) TO ASSEMBLE *****************
;
;   ************  THIS ASSEMBLER WILL CREATE A ( HEX ) FILE  **************


                ; 0B0H = PORT3 DIRECT ADDRESS
D_BUS DATA 0B0H ; data bus ( PORT 3 )

                ; 90H = PORT 1 DIRECT ADDRESS
A_BUS DATA 90H  ; address bus ( PORT 1 ),A0=P1.0,A1=P1.1,A2=P1.2

                ; 80H.0 = PORT 0 BIT 0 ( PORT0 BIT ADDRESS )
WR    BIT  80H.0; WR signal. to write to display A_BUS,data must be stable,
                ; then WR is brought LOW, data is written on LOW to HIGH
                ; transition of WR. so we then bring WR to HIGH to write.
                ; PORT 0 BIT 1 DIRECT BIT ADDRESS


A3    BIT  80H.1; clear for brightness set, then set and leave set.
                ; to set brightness send the following out to the data D_BUS.
                ; MSD-LSD 0=100% 1=80% 2=53% 3=40% 4=27% 5=20% 6=13% 7=blank

RST   BIT  80h.2; Display Reset

;***************************************************************************
;*          FIRMWARE  For Control Of The HDSP-2112 Display                 *
;*                    A  MOVING MESSAGE DISPLAY                            *
;*              FOR THE PHILLIPS 87C750 MICROCONTROLLER                    *
;***************************************************************************

org       0              ; Establish Reset Vector at 0

; Routine to Reset Display on Power-Up

          clr     D_BUS.7; Enable Display
          clr     RST    ; Reset & Clear Display
          setb    wr
          acall   delay2 ; No Read or Write for at least 3 clock cycles
                         ; after Reset & Clear
          setb    RST    ; Hold RST High for remainder of program

; Set Display Brightness


bright:   clr     a3     ; clr A3 to setup for brightness set
          mov     D_BUS,#7; data to blank display
          clr     wr     ; WR=LOW
          setb    wr     ; WR=HIGH, data written to display on LOW to HIGH
          mov     D_BUS,#6; 13% brightness
          clr     wr
          setb    wr
          setb    a3     ; transition of WR pin, then we leave A3 set for the
                         ; remainder of the program, as it is ONLY used to
                         ; tell the display we want to set BRIGHTNESS.

count:    mov     r7,#4  ; Load R7 with the number of times+1 you want your
                         ; message to be displayed before power down.
                         ; a 4 here will play the message 3 times etc...

count2:   djnz    r7,load    ; Decrement counter, if not=zero goto load
          ajmp    power_down ; else power down.

load:     mov     dptr,#message-1 ; load message address -1

begin:    mov     r0,#20h; beginning RAM address for storage + manipulation
          mov     r5,#8  ; #8=indicator of how many DIGITS the HDSP-2112 has
          mov     a,#20h ; ASCII equivalent of a BLANK space on display.

ramclr:   mov     @r0,a  ; load ASCII BLANKS in display RAM
          inc     r0     ; increment to next RAM address
          djnz    r5,ramclr ; if we havent BLANKED out 8 address's keep going

fetch:    acall   getchr ; RAM BLANK done , get first character to be diplayed

halt:     jz      count2 ; if return value in ACC = decimal 0 start over
          mov     r5,#8  ; number of display DIGITS available on HDSP-2112
          mov     r0,#20h; load beginning RAM address

doit:     xch     a,@r0  ; SWAP ACC data with display RAM data
          inc     r0     ; increment to next RAM address
          djnz    r5,doit; check if END of RAM location, if not keep going
          mov     r0,#20h; again load first RAM address
          mov     r4,#7  ; address to select first digit
                         ; ( far right ) on display
          acall   msgout ; send message digit to display
          ajmp    fetch  ; return to routine FETCH.

msgout:   clr     d_bus.7; re-enable display
          mov     r5,#8  ; load number of digits our display has for use.
                         ; notice here with R5 holding the starting value
                         ; of 8, that this allows the routine MSGOUT1 to
                         ; decrement R4 8 times. R4 originally holds the
                         ; address for digit #8, or the ( RIGHT MOST )
                         ; digit on our display. By decrementing R4
                         ; we move the display digit ( ADDRESS ) from
                         ; digit to digit.
                         ; or from digit 8 to digit 1, from RIGHT TO LEFT
                         ; as seen facing the display.
                ;NOTE:     ( IF WE CHANGE R5 TO 7 THE DISPLAY WILL SCROLL
                         ; TO DIGIT 2 THE SECOND FROM THE LEFT FACING THE
                         ; DISPLAY ).

msgout1:  mov     a,r4   ; load digit address for display digit selection
          mov     A_BUS,a ; select digit position on display
          dec     r4     ; 1st digit=7 ( right side of display ) decrement for
          mov     a,@r0  ; next, then load ACC with data to display.
          mov     D_BUS,a  ; move data to display
          clr     wr     ; WRITE STROBE for display
          setb    wr     ; write data to display on LOW to HIGH transition
          inc     r0     ; increment RAM pointer to next data digit for display
          djnz    r5,msgout1 ; if not=8 total digits keep going
          acall   delay2 ; delay to prevent JERKY look between digit updates.
                         ; and to set our display ( SCROLL SPEED ).
          ret            ; return to calling routine.

getchr:   inc     dptr   ; increment DPTR to point to next display digit
          clr     a      ; location ( MESSAGE ADDRESS ) in CODE space.
          movc    a,@a+dptr; move CODE ( MESSAGE ) digit pointed to by
          ret            ; ACC+DPTR too ACC, and return to calling routine.

power_down: mov   87h,#2 ; Set bit "PD" of the PCON Special Function Register
                         ; This will cause the controller to Power Down.


; routine DELAY2 sets the SCROLL SPEED, and will prevent a JERKY APPEARANCE
; between display digit updates. by changing the value first loaded into
; R1 in the first line to a lower number the scroll speed is faster, and by
; changing it to a higher number the scroll speed will be slower.

delay2:   mov     r1,#2
delay3:   mov     r2,#00h
delay4:   mov     r3,#00h
delay5:   djnz    r3,delay5
          djnz    r2,delay4
          djnz    r1,delay3
          ret
          nop


; the number 0 will indicate the END of our message.

message:  db      ' Merry Christmas..............,'
          db      ' And A Happy New Year..........',0



END