serial LCD 1602 Backpack using PIC16F690 for Hitach HD44780

[jackberg1]

Hello everyone,

I'de like to share this project, may come handy for hobbyist working around LCD display.

My search for a serial LCD that can receive serial data from 300 to 19200 baud on the internet was not successful
then I roll-up my sleeves and build this LCD backpack that use a common Hitachi HD44780 display. (still popular today)

My project was simple with parts already on hand like PIC16F690, NPN smd transistor, potentiometer, resistor. and PBP3 Basic code.

So enjoy,

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' Name  : 16F690 LCD BACKPACK
' Date  : Sep 27-2025
' Note  : 393 words used  of 2048
' Notes : Serin2 Baud Rate 300 ~ 19200 Intrc_OSC 8Mhz
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#CONFIG
cfg = _INTRC_OSC_NOCLKOUT 
cfg&= _WDT_OFF
cfg&= _PWRTE_OFF
cfg&= _MCLRE_OFF
cfg&= _CP_OFF
cfg&= _CPD_OFF
cfg&= _BOD_OFF
cfg&= _IESO_OFF
cfg&= _FCMEN_OFF
  __CONFIG cfg
#ENDCONFIG
DEFINE OSC 8        ' Core is running at EXT-CRYSTAL 16MHz PBP 33,217
ANSEL = 0           ' Set all pins digital
ANSELH = 0          ' Set all pins digital
OPTION_REG.7 = 0    ' PORTA/PORTB pull-ups are enabled by individual port latch values
CM1CON0 = 0         ' Analog comparators off


En var Portb.4 : low en
RS var Portb.6 : low rs
B1 var byte : b1 = 0


' 300=3313  600=1646  1200=813  2400=396  4800=188  9600=84  19200=32
BaudR var byte : baudr = 32 


TRISA = 0 : TRISB = 100000 : TRISC = 0
PORTA = 0 : PORTB = 0 : PORTC = 0
OSCCON = $70  


high Porta.0              ' Backlight ON


gosub LCDinit             ' initialise LCD


'Serin2
main:
    serin2 Portb.5,baudr,3,main,[b1]


    if b1 < 253 then     ' Characters
        PORTC = b1 
        HIGH EN : PAUSEus 5 : LOW EN
        goto main        
    elseif b1 = 254 then  ' LCD Command
        low RS            
        serin2 Portb.5,baudr,3,main,[b1]
        PORTC = b1          ' output the data
        HIGH EN : PAUSEus 5 : LOW EN
        high RS           ' character mode
        goto main         
    elseif b1 = 255 then  
        low rs            ' LCD Command


    serin2 Portb.5,baudr,3,main,[b1]
        if b1 = 0 then 
            low porta.0   ' Back Light OFF
        high rs
        endif
        if b1 = 8 then 
            high porta.0  ' Back Light ON
        high rs    
        endif
       goto main             ' loop back to top
    ENDIF


LCDINIT:                  ' Standard LCD Module Initialisation
PORTC = 000001          ' 2, Clear Display
    HIGH EN : PAUSEus 300 : LOW EN ' Send data
    pause 4
PORTC = 000010          ' 4, Return Home
    HIGH EN : PAUSEus 300 : LOW EN
    pause 4
PORTC = 111000         ' 1, 8 bit, 2 line, 5x8 Characters
    HIGH EN : PAUSEus 300 : LOW EN
    pause 4
' PORTC = 001100          ' Display on, no cursor, no blink
PORTC = 001110          ' 1, Display on, cursor, blink
    HIGH EN : PAUSEus 300 : LOW EN
    pause 4
PORTC = 000110          ' 1, Entry mode
    HIGH EN : PAUSEus 300 : LOW EN
    pause 4
    high rs                  ' character mode
RETURN

[jackberg1]

Here's an code update

on the LCD backpack code the line

BaudR var byte should be replace with: BaudR var Word

and here's the serial sender code updated as well. (use an 12F683)

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'Project : 12F683 Serial LCD Test 300 ~ 19200 baud for 16F690 Lcd Backpack
'Date    : Sep 27-2025
'Notes   : 285 words used  of 2048                                             
'Notes   : Serout2 300 ~ 19200  Intrc_OSC 8Mhz
'300=3313  600=1646  1200=813  2400=396  4800=188  9600=84  19200=32 
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#CONFIG
 __config  _INTOSCIO & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _BOD_OFF  & _CP_OFF & _CPD_OFF
#ENDCONFIG
DEFINE OSC 8           ' Core is running at EXT-CRYSTAL 16MHz PBP 33,217
LCD Var GPIO.0         ' Serial out
ANSEL = 0              ' Set all digital  PULLUP Resistor  page:10
TRISIO = %00000000     ' INPUT=1 OUTPUT = 0
OSCCON = $70           ' $70=8Mhz  $60=4mhz  $50=2MHZ  $40=1MHZ  $30=500KHZ   


BaudR var word
baudR = 32 ' 300=3313  600=1646  1200=813  2400=396  4800=188  9600=84  19200=32 
Pace var byte          ' for serout2 
pace = 0


SEROUT2 lcd,baudR,pace,[ 254, 1] ' Clear LCD
pause 40


DO
' LCD 1602
    sEROUT2 lcd,baudR,pace,[254,128,"ABCDEFGHIJKLMNOP"] ' Line 1 16 Char.
    SEROUT2 lcd,baudR,pace,[254,192,"0123456789-=,./>"] ' Line 2 16 Char.


' LCD 2004
    'SEROUT2 lcd,BaudR,pace,[254,128,"ABCDEFGHIJkLMNOPQRST"] ' Line 1 20 Char.
    'SEROUT2 lcd,BaudR,pace,[254,192,"0123456789-=,./;!@#$"] ' Line 2 20 Char.
    'SEROUT2 lcd,BaudR,pace,[254,148,"ABCDEFGHIJkLMNOPQRST"] ' Line 3 20 Char.
    'SEROUT2 lcd,BaudR,pace,[254,212,"0123456789-=,./;!@#$"] ' Line 4 20 Char.


    PAUSE 2000
    SEROUT2 lcd,baudR,pace,[ 255, 0] ' Back Light OFF
    PAUSE 200    
    SEROUT2 lcd,baudR,pace,[ 255, 8] ' Back Light ON
    PAUSE 2000
 
    SEROUT2 lcd,baudR,pace,[ 254, 1] ' Clear LCD
    pause 1000
LOOP
END

[jackberg1]

final code update in "16F690 LCD BACKPACK"
the low rs and high rs lines are not needed, since it control PortA.0 and not the HD44780 chip.

elseif b1 = 255 then
' low rs ' LCD Command
serin2 Portb.5,baudr,3,main,[b1]
if b1 = 0 then
low porta.0 ' Back Light OFF
' high rs
endif
if b1 = 8 then
high porta.0 ' Back Light ON
' high rs
endif

[Ioannis]

Thanks for posting your project.

But why not use the Hardware USART instead of the Software one?

Ioannis

[jackberg1]

Hello Ioannis,

good question,

when I design the PCB I used the PortB.5 with a 20Mhz crystal with bigger pcb foot print 46x17mm
then I decided to lower the parts count and the PCB foot print to a bare minimum (41 x 17mm)
Also theses HD44780 are still in use by many hobbyist around the world, I guess, and the baud rate I was looking is plenty for this kind of display.

thank's for asking.

[jackberg1]

Hello,

you're right
my assumption was that software or hardware control serial communication are the same
and one way or another I'll get the same result.

if I may ask in this project what the benefit of hardware over software serial control.

thank's again.

[Ioannis]

Less code usage. If for some reason you need Serin, it may hang if the device is not replying correctly. Hserin has timout and will save the day.

For your project it may not have any meaning, but I think it is good practice to use as much as you can the hardware features than the emulated software.

Ioannis

[richard]

if I may ask in this project what the benefit of hardware over software serial control.

doubtful there is any since the 690 does nothing else anyway and the lcd's speed is the real bottle neck

[jackberg1]

I aggree on both comment, Hserin is more convenient than Serin2

the goal of this project was to learn base on inexpensive parts on-hand

you can strech the total cost for less than $12 pcb included not bad for an hobbyist who's looking to add a simple but pratical alphanumeric display

I really appreciate comments

btw , what is happening with MELab Forum, is it close for good.

[Ioannis]

The Melabs Forum is(was?) supported by the company itself. So little is known as to what is happening.

The company does not really have a future.

Some of us here are also dinosaures and reluctant to switch to C or other platforms. So we stay and try to support its operation, as long as our host, honorable Lester, allows this forum to live.

Ioannis

[jackberg1]

very kind of you to reply,

Roughly 12 years ago, I started learning Basic Pic programming with Picaxe, then GCBasic
now I'm mostly using MELab PBP Pro, and Positron both are like twin of Pic Basic compiler.

my guess is these IDE Compilers are the last ones on the market, now the current trend is
with Arduino, Python etc..

if I may ask,

are you aware of any good sources on how,
to learn asm, and understand the asm files structure, to write assembler code, compile it and to download to a PIC

regards.

[Ioannis]

What is the use of learning ASM when C is better with great support and portable too?

I think it is a waste of time if you choose ASM. Also you have to deal with pages, Banks and will be very much difficult to keep your mind checking all the time if your code has to change banks, pages etc in order to access registers correctly.

But if you insist on diving in the deep dark waters of ASM, then I guess Microchip is the first to think. But these video tutorials also help https://www.youtube.com/@IESD2013

Ioannis

[jackberg1]

thanks for the advice, it's helping what to consider.

[jackberg1]

as for C is considered, which IDE/Compiler you use or recommend

[jackberg1]

quick update for the Backpack code: High RS line should be remove to avoid random character on screen when booting.

PORTC = %00000110 : High En : DelayUS 1 : Low En : DelayMS 1 ' Entry mode
' High RS
Return

[jackberg1]

correct order for display control

PORTC = %00001110 ' %00001DCB Display on/off, cursor on/off, blink y/n

[Ioannis]

Regarding C, MPLABX is the one to try and sure the last. It includes also the MCC tool to setup any microcontroller with ease.

Tried a couple of times C but i guess i am too old to change ...

Ioannis

[jackberg1]

I did try MPLAB X a year ago and it's was a bitter chalenge comparing to what I'm used to do with PBP3,Picaxe, Positron

[jackberg1]

Oct 2 2025

update on 16F690 Backpack, new LCDINT pause to accomodate 28800,38400 baud rate for (Xtal = 20Mhz)

#CONFIG
__config _HS_OSC & _WDT_OFF & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOD_OFF & _IESO_OFF & _FCMEN_OFF
#ENDCONFIG

LCDINIT: ' Standard LCD Module Initialisation
PORTC = %00000001 : HIGH EN : PAUSEus 1 : LOW EN : pause 4 ' Clear Display
PORTC = %00000010 : HIGH EN : PAUSEus 1 : LOW EN : pause 2 ' Return Home
PORTC = %00111000 : HIGH EN : PAUSEus 1 : LOW EN : Pause 2 ' 8 bit, 2 line, 5x8 Characters
PORTC = %00000110 : HIGH EN : PAUSEus 1 : LOW EN : Pause 2 ' Entry mode
PORTC = %00001110 : HIGH EN : PAUSEus 1 : LOW EN : Pause 2 ' %00001DCB Display on/off, Cursor on/off, Blink y/n
RETURN

[Ioannis]

Agree that MPLABX is a bit scarry but has all the tools to complete a task regarding C at least.

You have MCC, Simulator, breakpoints etc. Basic does not give all these goodies.

As for your LCD driver, I think it is a little bit dependant on the specific LCD characteristics. Some are slow and some are a bit faster, so user has take that into account.

Ioannis

[jackberg1]

totally agree, the LCD is kind of an old tech, but for an hobbyist it's a good learning tool.

to clarify the baud rate turn around, just include this chart to figure it out.

with each OSC setup, it can manage baud rate from 300 ~ 38400.