io.doc

一个C style Assembler的source code

             T h e   I O   k e y p a d / L C D   I n t e r f a c e

(0) OVERVIEW
   I often use a keypad/LCD unit with my 8051 stand-alone board to provide
an I/O interface.  This unit is configured in a specific way, and the io.lib
software assumes this specific configuration.

(1) HARDWARE INTERFACE
   (a) Memory Map
   The io.lib module assumes that the following registers are mapped to
EXTERNAL DATA memory (XBY memory, as referred to in the debugger) as
illustrated below:

                      Register                  Address
                      LR (LCD REGISTER)           e080
                      LD (LCD DATA)               e081
                      LS (LCD STROBE)            e090
                      KD (KEYPAD DATA)            e0a0

It assumes that the keypad input has an associated strobe which will trigger the
EXTERNAL INTERRUPT 1 pin (INT1) when INT1 is set in falling edge mode.

   (b) Keypad
   The keypad is assumed to have 16 keys on it.  When INT1 becomes active, the
lower order 4 bits of the KD register will contain the numeric code of the key
that was pressed,

   (c) Liquid Crystal Display (LCD)
   The LCD is assumed to be 4 rows by 20 columns.  The registers LR and LD are
used to sending commands, and sending data, respectively.  The strobe register,
LS, is used to latch data to or from either of these registers.

   To write to LD or LR, write to its memory-mapped address, and then toggle
the strobe, LS.  For example:

WriteLR:
   mov DPTR, #0e080h  ;;; Write A to LR
   movx @DPTR, A
   mov DPTR, #0e090h  ;;; Toggle LS.
   mov A, #1
   movx @DPTR, A
   mov A, #0
   movx @DPTR, A
ret

WriteLD:
   mov DPTR, #0e081h ;;; Write A to LD.
   movx @DPTR, A
   mov DPTR, #0e090h ;;; Toggle LS.
   mov A, #1
   movx @DPTR, A
   mov A, #0
   movx @DPTR, A
ret

ReadLR:
   mov DPTR, #0e080h  ;;; Clear out LR.
   movx A, @DPTR
   mov DPTR, #0e090h  ;;; Set LS to enable reading.
   movx @DPTR, #1
   mov DPTR, #0e080h  ;;; Read LR.
   movx A, @DPTR
   mov DPTR, #0e090h  ;;; Clear LS to complete the reading.
   movx @DPTR, #0
ret

ReadLD:
   mov DPTR, #0e081h  ;;; Clear out LD.
   movx A, @DPTR
   mov DPTR, #0e090h  ;;; Set LS.
   movx @DPTR, #1
   mov DPTR, #0e081h  ;;; Read LD.
   movx A, @DPTR
   mov DPTR, #0e090h  ;;; Clear LS.
   movx @DPTR, #0
ret

   The actual command codes used for the LCD will depend largely on the unit
itself, and have mostly been "encapsulated" in the IO interface software.  You
will need to make the appropriate changes to the IO routines for your LCD unit.

(2) IO FUNCTIONS
   The following is a description of the functions contained in the IO
interface.

   (a) Keypad routines
       key_init ... Initialize the keypad, set up external interrupt 1.
       cgetc ...... Read the keypad data into A.

   (b) LCD routines
       scr_init ... Initialize the display, and clear it.
       clear ...... Clear the display and set the cursor to row 0, column 0
       home ....... Set the cursor to row 0, column 0.

       set_cursor ... Set the cursor to the mode indicated in the register A.
                      A can be a combination of any of the following values:
                         DISPLAY_ON:   Turn the display on
                         CURSOR_ON:    Turn on the cursor.
                         CURSOR_BLINK: Make the cursor blink.
       cursor_left, cursor_right ... to move the cursor
       shift-left,   shift_right ... to move the display itself.
       locate ...... To place the cursor at the point indicated by the
                     variables Row and Col.
       save_cursor, restore_cursor:
                     So save and restore the more recent cursor
                     position
       cputc ....... Print the character in A out to the display in TTY manner.
       cputs ....... Print out an entire string, pointed to by DPTR, to the
                     display unit.
   (c) Variables
   The io.lib software uses 6 bytes of space for variables.  They have been
named as follows:

               Row, Col:       The current cursor position
               OldRow, OldCol: The most recent cursor position saved by the
                               last call to save_cursor.
               Counter: A 2-byte counter.