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Testing the PIC Microcontroller 63

Figure 6.19 Photograph of LCD display in self­test mode.

Home position (move cursor top left of display) 2
Move cursor one character position left 16
Move cursor one character position right 20
Scroll display one character position left 24
Scroll display one character position right 28
Set cursor position (DDRAM address) 128 � addr
Set point in character generator (CG) RAM 64 � addr
The onboard LCD also has a self­testing mode that will print the current
baud rate as determined by the jumper settings and mode (true/inverted); see
Fig. 6.19. To enter self­test mode, connect the serial in line to ground (for true)
or �5 V (for inverted) upon LCD module start­up.
Note: If the serial input line is improperly connected for self­test mode, for
instance connected to �5 V when jumpers are set for true mode, the LCD dis­
play will remain blank. The module stays in self­test mode as long as the ser­
ial input line is held either high (inverted mode) or low (true mode). LCD
module may be exited from self­test mode on the fly by simply connecting the
serial input line to a serial source.
When you print past the end of a line, the next 24 characters do not show
up on the LCD screen. They are not lost; they are in an off­screen memory
area. All alphanumeric LCD modules have 80 bytes of memory, arranged
appropriately for a 2 � 40 screen. On LCDs with smaller screens (such as
this 2 � 16), text printed past the end of a visible line goes into memory, but
can’t be seen on the screen. Use cursor­positioning instructions to print to a
particular location on the display. Or deliberately print in off­screen memo­
ry to temporarily hide text, then send scroll­left instructions to reveal it.

Using the LCD: PicBasic and PicBasic Pro examples
Connect the serial input of the LCD to portb.0 of a PIC microcontroller. The fol­
lowing PicBasic program demonstrates sending data and commands to the LCD.

main: pause 1000 ‘Wait for the LCD to start up
serout 0, t2400, ($fe,$01) ‘Clear the screen