A PIC Serial LCD project.

Learn about the tool used for creating this diagram.

Serial LCD Project
Compiler	Mikroelectronika C compiler V5.0.0.3 Free!
Target	16F877A (retargetable to other PICs that have enough pins and a built in USART).
Software level	Easy.
Software notes	Uses unget_char to reverse getchar action.
Hardware level	Easy.
Hardware notes	No special notes.
Project version 1.00	Initial Release
Project files	Enter your details to get the Download Link and get the microcontroller newsletter: Your Name: Primary E-Mail: (Note: Your email is safe it will never be sold or rented). You will get All the C source code and hex file.
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You can program the PIC in circuit through the ICSP connector.

For a tutorial on compiling these files click here.

You can recompile the serial LCD files if you want examine code operation (using the built in simulator) or change the source code. Note the hex file is contained in the download.

Serial LCD Command set

Serial LCD Command Set list (uses upper or lower case):

X and Y commands

You can also use the longer command:

#H#X00JFM

It does exactly the same thing but the cursor is immediately moved after the '00' since the command parser knows that it is the end of the X cursor position command as it only accepts 2 digits.

These  commands are valid:

Text entry

Serial LCD Hardware

The circuit simply consists of a PIC micro, ICSP interface, an RS232 level translator and an HD44780 LCD.

Serial LCD display Software

The software is contained in two files:

16F877A-serial-lcd.c
bit.h

bit.h contains bit manipulation macros.

Project Files

16F877A-serial-lcd.ppc

Output files:

16F877A-serial-lcd.hex

16F877A-serial-lcd.c

Initially a scrolling message is displayed using show_intro.  When  a serial input is detected the main program starts.  All keys are now either text entry or commands.

An infinite loop keeps checking for key input. If the key is a hash symbol then the command is fetched using:

get_prefix_and_execute_command(&x,&y);

Otherwise the key value is displayed on the LCD at the current cursor position.

Note: the use of x and y addresses (&x,&y) to pass the variable address through to the called functions so that values of x and y in main() are updated (using pointers in the called functions).

get_prefix_and_execute_command calls execute_command which gets another key from the USART (or waits for one).  If it matches a valid command then the appropriate code is executed to control the LCD.  If not then USART_unget_char is used to push the key back.

The most interesting commands in execute_command are #X and #Y which use get_and_Set_X and get_and_Set_Y, again using pointers (this time the address & de-reference is not used as px is a pointer that returns its address when invoked).  

These functions both use get_2dig_num which gets more characters expecting digits - if it does not get them it pushes the key back again using USART_unget_char.

USART_get_char, USART_unget_char

These complementary functions are used in parsers (this program is a very small parser) where you need to look at the next character of the input to see if you want to continue. If you don't i.e. its not the character you were expecting then you use unget_char to put the current character into memory.  

get_char always checks this memory first before getting a character from its normal input so the system works well - but you can only do one ungetchar at a time.  For more you would need an array of unget storage etc.

The routines let you avoid complicated look ahead algorithms or indexing - you can concentrate on the current character without knowing where an index is.  For a bigger parser you work with complete words.