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                                 CHAPTER 8

                                  _______
                                  DISPLAY



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8.1  HARDWARE

     The display used in the Organiser II is a Hitachi LR039 Liquid Crystal
Display (LCD) driven by a Hitachi HD44780 LCD controller.

     It consists of two lines of 16 characters.  Each character is  defined
by  a  5 x 8 dot matrix with the 8th line normally left blank as it is used
for the single line cursor.

     The character generator in the LCD controller contains 192 displayable
characters  (ASCII  values  32  to  256).   There are also 8 user definable
characters which are repeated twice in the character set ASCII values 0  to
7 and 8 to 15.

     The full specification and operation of the controller is given in the
accompanying data book "Hitachi MOS LSI Data Book, LCD Driver LSI" on pages
79 to 128.  It is recommended that this be read for a full understanding of
the LCD.

     A full hardware description of the LCD and controller  is  in  section
2.7.



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8.2  SOFTWARE

     As described in the LCD  Data  Book  the  LCD  controller  contains  a
control register and a data register.  These are accessed via the following
addresses:-


     $0180      SCA_LCDCONTROL          The LCD control register

     $0181      SCA_LCDDATA             The LCD data register



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8.2.1  EXAMPLE

     The following machine code program stores a pound sign in UDG 0 (ascii
characters  0  and  8).   The  data for the pound sign is read from address
DATA.


SAVUDG:
; Set LCD address to $40 the address of the first UDG.
        LDA     A,#$40          ;A is LCD address
; Wait for busy low.
1$:     TST     SCA_LCDCONTROL
        BMI     1$
; Store address
        STA     A,SCA_LCDCONTROL
; Now store data
        LDX     #DATA
        LDA     B,#8
2$:     LDA     A,0,X
; Wait for busy low.
3$:     TST     SCA_LCDCONTROL
        BMI     3$
; Store data. (LCD address auto increments)
        STA     A,SCA_LCDDATA
        INX
        DEC     B
        BNE     2$
        RTS

DATA:
        FCB     6,9,9,12,8,24,31,0      ;Pattern for pound sign



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8.2.2  VARIABLE USAGE

     The following variables are used by the display system services:

    dpt_tlin    16 byte buffer containing contents of top line of
                the display.
    dpt_blin    16 byte buffer containing contents of bottom line of
                the display.
    dpb_cpos    Current cursor position (0-31)
    dpb_cust    Cursor state (as passed in DP$STAT)
    dpb_vlin    Used in view
    dpb_vsiz    Used in view
    dpb_vdir    Used in view
    dpw_sped    Horizontal scrolling rate (in 50ms intervals)
                Delay before scrolling is four times dpw_sped
    dpw_dely    Vertical scrolling rate.
    dpw_redy    Decremented every 50ms. Used for timing. See DP$WRDY.
    dpa_vadd    Used in view.
    dpb_spos    Saved cursor position. Used by DP$SAVE and DP$REST.
    dpb_scus    Saved cursor state. Used by DP$SAVE and DP$REST.
    dpt_save    32 byte buffer containing saved display text. Used by
                DP$SAVE and DP$REST.



     _______________
8.3  SYSTEM SERVICES

     This section describes the operating system calls for writing  to  the
LCD display.



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8.3.1  DP$STAT

VECTOR NUMBER:         020
INPUT PARAMETERS:      A register - Cursor position 0 - 31.
                       B register - Cursor status.
OUTPUT VALUES:         None


DESCRIPTION


    Displays the cursor at position A register and according
    to the B register as follows : -

        Bit 7 - On  = Display cursor.
                Off = Remove cursor.
        Bit 0 - On  = Display the cursor as a line.
                Off = Display the cursor as a block.
    The new cursor position is stored in dpb_cpos and the new cursor  state
    is stored in dpb_cust by this routine.

EXAMPLE

;       Move the cursor to the 2nd position on the 2nd line (position 17)
;       and display as a block cursor

        LDA     A,#17
        LDA     B,#$80
        OS      DP$STAT


ERRORS:                None



       _______
8.3.2  DP$VIEW

VECTOR NUMBER:         021
INPUT PARAMETERS:      A register - 0 for top line or 1 for bottom line.
                                    If the top bit is set then the routine
                                    will not allow the use of any arrow
                                    keys and will return on any key press.
                       B register - Length of string to view
                       X register - Address of string to view
                       UTW_S0     - Time to delay before scrolling
                                    in 1/20 second.

OUTPUT VALUES:         B register - Key press that terminated scrolling.


DESCRIPTION


         Displays the string  and  then  starts  to  scroll  to  the  right
    wrapping  around  with  two spaces in between, on the line specified in
    the A register.

         The A register is ANDed with 1 so that values of 2,4 etc would all
    indicate the top line.

         Pressing the left and right arrow keys alters the scrolling action
    if top bit of A register is clear when passed to the routine.

         Any other key press is returned in the B register.

         If the returned key is not of interest and scrolling of  the  same
    string is to be continued then VIEW can be called again with an address
    of 0 in the X register.  No other calls to the display driver should be
    used between the subsequent calls of DP$VIEW with X = 0.

         The cursor is switched off during  this  routine  but  the  cursor
    state prior to the call is maintained.

         After this call the cursor position as used by the PRINT and  EMIT
    routines will be trashed.

         Corrupts location dpb_cpos the current cursor position.

EXAMPLE

    The following example displays the first 16 characters of the string
    "HELLO THERE PLEASE PRESS EXECUTE" for 2 seconds on the second line
    of the LCD. Then continually scrolls the whole string until the
    execute key is pressed. Pressing the arrow keys will stop, start
    and change the direction of the scrolling.

DISP:
        LDD     #40
        STD     UTW_S0                  ; wait 2 seconds before scrolling
        LDA     A,#1                    ; display on second line
        LDX     #STRING                 ; address of string
        LDA     B,#ENDSTR-STRING        ; length of string
1$:
        OS      DP$VIEW
        LDX     #0                      ; continue viewing unless
        CMP     B,#13                   ; execute key was pressed
        BNE     1$                      ; if so return
        RTS

STRING:
        .ASCII  "HELLO THERE PLEASE PRESS EXECUTE"
ENDSTR:

ERRORS:                None.

BUGS

    If the string is less than the screen width then no scrolling
    will occur but the routine will still wait for a key and will
    discard left and right arrow key presses.

    If a call is made initially with the X register equal to 0
    then anything can and probably will happen.



       _______
8.3.3  DP$PRNT

VECTOR NUMBER:         017
INPUT PARAMETERS:      B register - Number of characters to print.
                       X register - Address of string to be printed.
OUTPUT VALUES:         None.


DESCRIPTION


         Prints B characters from X one at a time using DP$EMIT.

EXAMPLE

    The following example clears the top line and then prints
    "TOP LINE" on the top line.


        LDX     #STRING
        LDA     B,#ENDSTR-STRING
        OS      DP$PRNT
        RTS

STRING:
        .BYTE   $0E
        .ASCII  "TOP LINE"
ENDSTR:

ERRORS:                None.



       _______
8.3.4  DP$EMIT

VECTOR NUMBER:         016
INPUT PARAMETERS:      A register - Character to be emitted.
OUTPUT VALUES:         None.



DESCRIPTION


         Outputs a character to the LCD display.  Control characters  ASCII
    0 to 7 display the 8 user definable graphics characters.

         The buffers dpt_tlin or dpt_blin are updated by  this  routine  to
    give an accurate reflection of what is actually on the screen.

         The  cursor  position  is  automatically  incremented   when   any
    displayable  (i.e.  non control characters) are output.  When the cursor
    reaches the end of the top line it will wrap around to the beginning of
    the  bottom  line.   When the cursor reaches the end of the bottom line
    the bottom line will be scrolled to the left.

         Certain of the ASCII control characters are  intercepted  by  this
    routine to control the display as follows :-

      ASCII DEC HEX OCT DESCRIPTION

        BS   8  08  10  Moves cursor left 1 character.
        HT   9  09  11  Moves cursor to the nearest position modulo 8.
        LF  10  0A  12  Goes on to the next line.
        VT  11  0B  13  Moves the cursor to the top left of display.
        FF  12  0C  14  Clears both lines of the display.
        CR  13  0D  15  Returns the cursor to the beginning of line.
        SO  14  0E  16  Clears the top line. Cursor at top left.
        SI  15  0F  17  Clears the bottom line. Cursor at bottom left.
        DLE 16  10  20  Rings the bell.
        DC1 17  11  21  Refreshes display from the top and bottom buffers.
        DC2 18  12  22  Refreshes display from the top buffer.
        DC3 19  13  23  Refreshes display from the bottom buffer.

 Refreshing the top buffer is done by redisplaying the data in dpt_tlin.
 Refreshing the bottom buffer is done by redisplaying the data in dpt_blin.

EXAMPLE

    The following example refreshes the display on the top line, clears
    then displays the character "?" on the bottom line.

        LDA     A,#$12
        OS      DP$EMIT         ; redisplay top line
        LDA     A,#$0F
        OS      DP$EMIT         ; clear bottom line
        LDA     A,#$3F
        OS      DP$EMIT         ; display question mark
        RTS

ERRORS:                None.



       _______
8.3.5  DP$SAVE

VECTOR NUMBER:         019
INPUT PARAMETERS:      None.
OUTPUT VALUES:         None.


DESCRIPTION


         Saves the current screen state including the cursor  position  and
    status in the following variables:-

    dpb_spos    Saved cursor position.
    dpb_scus    Saved cursor state.
    dpt_save    32 byte buffer containing saved display text.

         Note that since this routine saves the screen state  in  a  static
    buffer, calls to DP$SAVE and DP$REST cannot be nested.

         Note that this routine should not  be  called  unless  alarms  are
    disabled  as  the  alarm  software calls this routine as well.  This is
    explained in section 19.3.  Also the pack sizing routine (PK$SETP) uses
    these calls when displaying "SIZING PACK B" etc.


ERRORS:                None.




       _______
8.3.6  DP$REST

VECTOR NUMBER:         018
INPUT PARAMETERS:      None.
OUTPUT VALUES:         None.



DESCRIPTION


         Restores a previously saved copy  of  the  screen  from  dpb_spos,
    dpb_scus and dpt_save.  See DP$SAVE.


ERRORS:                None.

BUGS

    If DP$REST is  called  without  previously  calling  DP$SAVE  then  the
    results will be unpredictable.



       _______
8.3.7  DP$WRDY

    VECTOR NUMBER:         022
    INPUT PARAMETERS:      None.
    OUTPUT VALUES:         None.



    DESCRIPTION


         Waits until the value in dpw_redy has been decremented to 0.

         Each keyboard interrupt causes dpw_redy to be decremented by 1 and
    as  such  provides a handy 50 millisecond timer.  However if interrupts
    are switched off this routine will still work  as  it  recognises  that
    interrupts are off and decrements dpw_redy once every 50 milliseconds.

         Note that this routine behaves as a wait on a timed semaphore.  It
    is  used  extensively  by  the LCD driver software to provide scrolling
    delays.

EXAMPLE

    The following routine waits for 3 seconds

        LDD     #60
        STD     DPW_REDY
        OS      DP$WRDY
        RTS


ERRORS:                None.