Erratic behavior with a PIC16F88 and an custom LCD Board
I am having trouble with a custom LCD controller board I am trying to build.
Here is the background information:
- Attached is the schematic: (LCD_PIC16F88_PCB.jpg).
- I am using a 20Mhz resonator from HobbyEngineering (http://www.hobbyengineering.com/H1471.html).
- On the bottom of the post is my code - it is based off the LCD.bas sample.
- The B R D on the board represent Ground, +5V and Data respectively using a standard servo cable.
- I am using MicroCode Studio version 2.3.0.0, melabs Programmer software version 4.01 and a USB2 Programmer (http://www.melabs.com/products/usbprog.htm).
- I am programming with PicBasic Pro version 2.46
- I am using the following 16x2 backlit LCD (http://www.jameco.com/Jameco/Products/ProdDS/365982.pdf)
- this is my first attempt at a custom carrier board for any PIC.
The problem is that sometimes the thing works and sometimes it does not. When I first power on the circuit, it will either work or just show the top row as all black. The all black just means that the unit is powered on but has not received any direction from the microcontroller yet. I can accomplish the same thing by just powering the circuit on with no microcontroller in place.
To make sure it is not the code or the LCD or the pic, I am also using a PicoProto 18L prototyping board (http://www.melabs.com/downloads/pp18l_06.pdf) which is using the same resonator I’ve mentioned above. The whole thing works flawlessly every time out of the gate on the PicProto board.
Given this much, I figured maybe a bad resonator or a bad power supply. I changed the resonator with another one I had and that did not fix the problem - still getting erratic behavior.
I have several in progress projects that have a regulated 5v power output and tried the circuit connected to three or more of those (including the power on the PicProto 18L). To no avail.
I checked the circuit for bad etched copper lines and solder, re soldered a few things, dremmeled a few lines that looked too close, etc. All to no avail.
I am sure I am missing something simple that will be bright and blinding to the eyes of experience. Right now, I only see shadows …
Any suggestions, observations, comments, complements or insults anyone may be able to tender to help out would be very much appreciated.
Thanks in advance ...
Russ
----- not so brilliant code here ... ----
' PicBasic program to demonstrate operation of an LCD in 4-bit mode
'
' LCD should be connected as follows:
' LCD PIC
' DB4 PortA.0
' DB5 PortA.1
' DB6 PortA.2
' DB7 PortA.3
' RS PortA.4 (add 4.7K pullup resistor to 5 volts)
' E PortB.3
' RW Ground
' Vdd 5 volts
' Vss Ground
' Vo 20K potentiometer (or ground)
' DB0-3 No connect
@ DEVICE PIC16F88, HS_OSC 'HS oscillator
@ DEVICE PIC16F88, WDT_ON 'Watchdog Time
' (http://www.hobbyprojects.com/pic_tut...utorial13.html)
@ DEVICE PIC16F88, PWRT_ON '15.5 Power-Up Timer: Provides a fixed delay of
' 72 ms (nominal) on power-up only. It is designed to keep the
' part in RESET while the power supply stabilizes.
@ DEVICE PIC16F88, BOD_ON '15.7 Brown-Out Detect
@ DEVICE PIC16F88, MCLR_ON 'Master Clear Options set to Internal. RA5 unavail
@ DEVICE PIC16F88, LVP_OFF '15.18 Low Voltage Programming via ICSP.
@ DEVICE PIC16F88, CPD_OFF '15.1 bit 8 - Data EE Memory Code Protection bit
@ DEVICE PIC16F88, WRT_OFF '15.1 bit 10-9. FLASH Program Memory Write protection off
@ DEVICE PIC16F88, DEBUG_OFF '15.1 bit 11. DEBUG: In-Circuit Debugger Mode bit
' In-Circuit Debugger disabled, RB6 and RB7 are general
' purpose I/O pins
@ DEVICE PIC16F88, CCPMX_OFF '15.1 bit 12. CCPMX: CCP1 Pin Selection bit
' 1 = CCP1 function on RB0
' 0 = CCP1 function on RB3
@ DEVICE PIC16F88, PROTECT_OFF 'Code protection off
'Command Operation
'$FE, 1 Clear display
'$FE, 2 Return home (beginning of first line)
'$FE, $0C Cursor off
'$FE, $0E Underline cursor on
'$FE, $0F Blinking cursor on
'$FE, $10 Move cursor left one position
'$FE, $14 Move cursor right one position
'$FE, $80 Move cursor to position 0 (+offset to precisly posn)
'$FE, $C0 Move cursor to beginning of second line (+offset to precisly posn)
'$FE, $94 Move cursor to beginning of third line
'$FE, $D4 Move cursor to beginning of fourth line
define OSC 20
OSCCON=%01110000 ' pg 41. Setting bit 1-0: 00 = Oscillator mode defined by FOSC<2:0>
TRISB=%00000000 ' all portb to output
TRISA=%00000000 ' all porta to output
ANSEL=%00000000 ' set all analog pins to digital
pinLED var portb.4 ' blink and stuff to know we're alive
I var word
high pinLED
Pause 1500 ' Wait for LCD to startup
loop:
low pinLED
Lcdout $FE, 1, "Russ was here ..."
pause 1000
lcdout $FE, $C0, " or was he ..."
pause 4000 ' Give that some time to sink in.
lcdout $FE,1 ' Clear screen
lcdout $FE, $C0, "Second line ..."
pause 500
lcdout $FE, 2, "First line ..."
pause 500
lcdout $FE, 1 ' Clear the screen again - we love to clear screens.
pause 500
lcdout $FE, $80, "Dec:"
lcdout $FE, $C0, "Hex:"
for I = 0 to 199
lcdout $FE, $80+5, dec3 I
lcdout $FE, $C0+5, hex3 I
toggle pinLED
pause 200
next I
pause 1500 ' Alone done - take a quick breather.
Goto loop ' Start all over again.
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