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sturnfie
Joined: 26 Apr 2010
Posts: 17
Location: Palatine, IL
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| LCD using flex.c only writes first 8 characters then freezes |
 Posted: Thu Sep 16, 2010 5:04 pm |
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Hi all,
I'm using a PIC18F4620 to drive a NHD-0420DZ-FL-Y8W in 4-bit mode. I am using the flex.c driver for the 4x20 display.
If I write all o's (code: 01101111) to the screen, I will only see the first 8 or 9 (the exact count seems to be random). If I ground Data7 of the LCD, I will see all 80 o's. If I loop the printing of the o's, I will see 80 g's (01100111) when the data7 line is grounded, but will see 8 or 9 o's when it is not.
I've combed this forum (and others), but after trying various suggestions, I haven't found a functional solution. A solution of using a transistor to GND DATA7 will allow the entire display to be written to, but will limit the usable command/character set to those with (bit7,bit3) = 0.
The display obviously sees DATA7 (as the o is displayed correctly in the first positions), but something is freezing the display until DATA7 is pulled LOW.
This behavior is seen irregardless of which pins are allocated for the LCD interface. Also, #USE STANDARD_IO(ALL) is set.
I'd love to hear any suggestions.
Lucas |
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Thu Sep 16, 2010 5:16 pm |
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Not familiar with the display, but can/have you tried using it in 8 bit mode?
Perhaps using another port from the PIC(setup/perhiperal issues ?)
If it works OK in 8 bit mode, then maybe there is a driver issue, some quirk with that display? |
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sturnfie
Joined: 26 Apr 2010
Posts: 17
Location: Palatine, IL
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| Posted: Thu Sep 16, 2010 6:30 pm |
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| temtronic wrote: | Not familiar with the display, but can/have you tried using it in 8 bit mode?
Perhaps using another port from the PIC(setup/perhiperal issues ?)
If it works OK in 8 bit mode, then maybe there is a driver issue, some quirk with that display? |
8-bit mode does work. However, my application doesn't have available I/O pins beyond the 7 currently allocated. I really want to get 4-bit mode working. I've tried various other ports/pins on the PIC, with the same results each time. I guess I can use some kind of shift register to keep the pin count down...
What I'm hoping for is that someone else has seen a similar issue and can make a recommendation. The confounding part of this problem is that everything seems to work when that DATA7 line is grounded.
Lucas |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Sep 16, 2010 7:11 pm |
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Does your schematic look like the 4-bit schematic on page 4 of the
LCD data sheet ?
http://www.newhavendisplay.com/specs/NHD-0420DZ-FL-YBW.pdf
Post a short, complete, compilable test program that shows the problem.
Don't post the Flex lcd driver. Just #include it in your program.
Post the list of #define statements at the top of the Flex driver, that
define the connections between the PIC and the LCD. Also post the
#define statement concerning the R/W line.
Also post your compiler version. |
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sturnfie
Joined: 26 Apr 2010
Posts: 17
Location: Palatine, IL
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| Posted: Thu Sep 16, 2010 8:10 pm |
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| PCM programmer wrote: | Does your schematic look like the 4-bit schematic on page 4 of the
LCD data sheet ?
http://www.newhavendisplay.com/specs/NHD-0420DZ-FL-YBW.pdf
Post a short, complete, compilable test program that shows the problem.
Don't post the Flex lcd driver. Just #include it in your program.
Post the list of #define statements at the top of the Flex driver, that
define the connections between the PIC and the LCD. Also post the
#define statement concerning the R/W line.
Also post your compiler version. |
The schematic is identical to the wiring of my circuit. Compiler PCH v4.106
The following code will display the error. When voltage is applied, the display will show 8 or 9 "o"s. If a GND connection is made to DATA7 after initialization, the full 80 "o"s will be seen. Modifying the loop to continously print "o"s will show all "g"s when DATA7 is GND, and only 8 or 9 "o"s when DATA7 is in a standard configuration. If a GND connection is made to DATA7 before initialization, the display will show two lines of block characters.
| Code: |
#include "18F4620.h"
#include "flex.c"
#FUSES NOWDT
#FUSES HS
#FUSES NOPUT
#FUSES NOPROTECT
#FUSES NOBROWNOUT
#FUSES NOLVP
#use delay(clock=20000000)
#define USE_RW_PIN 1
#define LCD_DB4 PIN_B4
#define LCD_DB5 PIN_B5
#define LCD_DB6 PIN_B6
#define LCD_DB7 PIN_B7
#define LCD_RW PIN_B2
#define LCD_RS PIN_B1
#define LCD_E PIN_B0
void main()
{
disable_interrupts(GLOBAL);
lcd_init();
byte i = 0;
lcd_putc("\f");
for(i=0; i<80; i++){
if(i ==21 || i == 41 || i==61){
printf(lcd_putc, "\n");
}
printf(lcd_putc, "o");
}
while (true) {}
}
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Sep 16, 2010 8:16 pm |
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| Quote: |
#define USE_RW_PIN 1
#define LCD_DB4 PIN_B4
#define LCD_DB5 PIN_B5
#define LCD_DB6 PIN_B6
#define LCD_DB7 PIN_B7
#define LCD_RW PIN_B2
#define LCD_RS PIN_B1
#define LCD_E PIN_B0
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Pins B6 and B7 are used by the ICD debugger/programmer. Do you
have a debugger or programmer plugged into the board ? Does your
board have a built-in ICD ?
Try using two other PIC pins for DB6 and DB7, other than B6 and B7. |
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sturnfie
Joined: 26 Apr 2010
Posts: 17
Location: Palatine, IL
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| Posted: Thu Sep 16, 2010 8:24 pm |
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| PCM programmer wrote: | | Quote: |
#define USE_RW_PIN 1
#define LCD_DB4 PIN_B4
#define LCD_DB5 PIN_B5
#define LCD_DB6 PIN_B6
#define LCD_DB7 PIN_B7
#define LCD_RW PIN_B2
#define LCD_RS PIN_B1
#define LCD_E PIN_B0
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Pins B6 and B7 are used by the ICD debugger/programmer. Do you
have a debugger or programmer plugged into the board ? Does your
board have a built-in ICD ?
Try using two other PIC pins for DB6 and DB7, other than B6 and B7. |
I've used A1/A0 and D7/D6 as alternatives to B7/B6. Same result each time. Coincidently, I discovered that grounding DATA7 allows some level of operation when I left my PICKIT2 connected, with the USB disconnected, and noticed the entire display filling with characters (PICKIT2 has pulldowns on PGC/PGD, and shares GND with circuit).
Anyway, the ICSP does not seem to be the cause of these particular troubles.
Lucas |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Sep 16, 2010 8:48 pm |
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Try using the CCS lcd driver for 4x20 lcds:
| Quote: | | c:\program files\picc\drivers\lcd420.c |
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sturnfie
Joined: 26 Apr 2010
Posts: 17
Location: Palatine, IL
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| Posted: Thu Sep 16, 2010 9:55 pm |
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| PCM programmer wrote: | Try using the CCS lcd driver for 4x20 lcds:
| Quote: | | c:\program files\picc\drivers\lcd420.c |
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This worked. Thank you!
For anyone else encountering this error, this suggestion worked with the test example I posted above, with minor modifications. First I had to change the NOPUT to PUT (use Power Up Timer, otherwise the display didn't initialize properly) and secondly I included the lcd420.c file instead of the flex.c file.
Also, the compiler was complaining (with some cryptic error code) about the switch statement in the lcd_gotoxy function (of lcd420.c) not having a default case. Adding one will make that error go away and allow for a successful build.
Lucas |
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