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Connecting a 2-line-LCD to a STK500 port
The develloper board STK500 doesn't come with a LCD interface for connecting a cheap
display, like STK200 does. But even the STK200-LCD-port has some disadvantages: It
requires talking to the LCD in memory mapped mode, which means, that the LCD interface
blocks external SRAM space and requires slowing down the CPU with extra wait states. But
it is easy to connect such a display to a port of the processor directly, without using
memory mapping. It requires only 6 port bits, and the software is very easy, if you skip
reading the display memory. The data sent to the LCD is divided in packages to 4 bits
each. Hardware is rather easy, too. One disadvantage is that you have to do the timing
without reading the display's enable bit, requiring some adjusted delay loops. But that
is not too bad.
The hardware is shown in the following scheme:
So its only connecting the correct
That's all for the hardware.
- Port-Bit to the appropriate LCD-Pin,
- voltage source pins to the ones on the LCD display, and the correct
- pot pins to the contrast adjustment pins of the LCD.
The software for talking to the LCD is completely separated in the file
LCD4INCE.html in HTML-format and in the file
Lcd4IncE.asm in source file format.
The following routines are provided:
The software can be included in an existing program. The header in the file
lists the requirements, that the source file must fulfil to work correctly
with the LCD rountines.
- Lcd4Init: This routine resets the LCD,
- Lcd4Chr: This displays the char in rmp on the LCD,
- Lcd4PBcd: This displays the packed BCD in rmp on the LCD,
- Lcd4ZTxt: This displays the null-terminated text in the flash memory on the LCD, using the Z pointer,
- Lcd4RTxt: This displays rmp chars in SRAM where Z points to.
As a demonstration and test program a software clock has been programmed.
This program displays date and time of a software clock on the LCD. The
program is listed in the file
LCDINCCE.html in HTML-format and in the file
Lcd4IncCE.asm in source format.
Sorry that you currently can not adjust the clock. If you like, you can
add some lines of code to use the switches or the UART via the PC to adjust
the software clock.
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