Odometer Effect with
BPI- and BPK-series Displays

The LCD Serial Backpack^® gives you direct access to all LCD capabilities via a convenient serial connection. One often-overlooked LCD feature is the custom symbol set. By downloading data (bit patterns) to character-generator RAM you can change the appearance of up to eight special symbols. See Backpack app note 2 for more information.

This BASIC Stamp 2 program shows how to use one custom character to produce a useful and attractive animation effect that simulates the vertical scrolling of the last digit of an odometer.

' Program: ODO1.BS2 ("Odometer" style display on 2x16 Serial LCD)
' Contributed by: Scott Edwards. 
' Configure display for 9600 baud; serial in to BS2 P0. 

' This program demonstrates an interesting animation effect on a 
' 2x16 LCD equipped with the LCD Serial Backpack (R) interface. 
' It displays an on-screen counter whose lowest digit 'rolls up' 
' just like the tenths-of-a-mile digit in a car's mechanical 
' odometer. The effect was actually inspired by jackpot displays
' in Las Vegas, which use a similar effect. 

' The technique for producing this effect relies on a little-known 
' aspect of the LCD's CG (character generator) RAM. Alphanumeric 
' LCDs give you 8 symbols whose bit patterns are stored in CG RAM. 
' Writing to CG RAM changes the appearance of the symbol corresponding
' to the RAM address. The subtle thing is that when you write to CG 
' RAM you change the bit pattern of symbols already displayed on the 
' screen. For example, if your display shows symbol 0 in five different
' locations, changing symbol 0's bit pattern would alter all five 
' instances of the character. 

' In this application, we use symbol 0 as the final digit of a 
' counter. Symbol 0 is initially defined with the bit pattern for 
' "0". Each time the count increments, the program scrolls upward
' one position in an 80-byte table of bit patterns for the numbers 
' "0" through "9". The visual effect is that the last digit of the 
' counter rolls upward from one digit to the next. When it rolls
' from 9 to 0, the ones digit of the main counter increments. 

' ==== TABLE OF BIT PATTERNS
' This table contains the bit patterns for the numbers 0-9 in the format
' used for LCD custom characters. There are a total of 80 bytes in this
' table. 
zero	data	$E,$11,$13,$15,$19,$11,$E,$0
one	data	$4,$C,$4,$4,$4,$4,$1F,$0
two	data	$E,$11,$11,$2,$4,$8,$1F,$0
three	data	$1F,$2,$4,$2,$1,$11,$E,$0
four	data	$2,$6,$A,$12,$1F,$2,$2,$0
five	data	$1F,$10,$1E,$1,$1,$11,$E,$0
six	data	$6,$8,$10,$1E,$11,$11,$E,$0
seven	data	$1F,$1,$2,$4,$8,$8,$8,$0
eight	data	$E,$11,$11,$E,$11,$11,$E,$0
nine	data	$E,$11,$11,$F,$1,$2,$6,$0

' ==== CONSTANTS
n9600	con	$4054	' Baudmode for 9600 bps inverted serial. 
I	con	$FE	' Instruction prefix
CG	con	64	' Base address of custom-character 0. 
DD	con	128	' Base address of display RAM. 
clrLCD	con	1	' Clear-screen instruction. 
cntrPos	con	196	' Screen location of the counter.

' ==== VARIABLES
patPntr	var	byte	' Pointer into the EEPROM data. 
index	var	nib	' Counter variable for loading 8 bytes to CG RAM.
LCData	var	byte	' Data for xfer to the LCD. 
mainCnt	var	word	' Main counter

' ==== STARTUP
' To begin, the program waits a second to allow the display to 
' initialize, then clears the screen and displays the title "Odometer
' Effect". It then executes updateCnt to display the counter. 
pause 1000
serout 0,n9600,[I,clrLCD]	' Clear the screen. 
pause 10			' Wait a moment for clear to finish. 
serout 0,n9600,["Odometer Effect"]	' Print the title. 
gosub updateCnt			' Put the counter on screen. 

' ==== MAIN PROGRAM LOOP
' This loop uses a pair of subroutines to scroll the last digit of 
' the counter upward (xferPattern) and to update the state of the 
' main, 5-digit counter (updateCnt). When the last digit has scrolled
' upward to the point that "9" rolls over to "0" it's time to increment
' the main counter. It takes 80 loops to go through the whole scrolling 
' animation, so the main counter increments at 1/80th the loop rate. 
' In an actual application, you'd probably need to use a little math 
' to adjust the relationship of the scrolling rate to the event being 
' counted. 
again:
  gosub xferPattern		' Define the bit pattern. 
  if patPntr <> 80 then skip1	' When we hit 80, increment the 
  gosub updateCnt		' main counter. 
skip1: 
  pause 50			' Slow down a little to avoid blur.
goto again			' Run continuously. 

' ==== SUBROUTINE: updateCnt
' Prints the 5-digit counter value at cntrPos, followed by the 
' animated symbol (ASCII 0). Strictly speaking, it's not 
' necessary to keep reprinting the symbol, but doing so in 
' this subroutine saves us the trouble of using a separate 
' Serout to print the symbol the first time. --After displaying
' the counter, updateCnt adds 1 to it and resets the animation 
' point to the beginning of the bit patterns. 
updateCnt:
  serout 0,n9600, [I,cntrPos,DEC5 mainCnt,0]
  mainCnt = mainCnt + 1
  patPntr = 0
return

' ==== SUBROUTINE: xferPattern
' Transfers the current bit pattern to CG memory. 
xferPattern: 
  serout 0,n9600,[I,CG]		' Go to CG RAM. 
  for index = 0 to 7		' Load 8 bytes of character pattern. 
   read ((patPntr + index) //80), LCData	' Get byte from EEPROM. 
   serout 0,n9600,[LCData]	' Send it to CG RAM. 
  next				' Send all 8 bytes. 
  patPntr = patPntr+1		' Point to next location in table. 
return