LCD works at 4MHz, but not 12 or 16MHz

Hello helpful people!

I wrote (well..copied, pasted, and hacked) a program to simply spit out some messages to a LCD. It works great with the internal or external 4MHz clock. But when I try to use a faster clock, there are some good characters, but also some garbage displayed on the LCD.

I'd like to increase the clock speed because eventually I would like to interface with a RFID reader Ic where the Rx data transmission rate is 15625 baud async. So I picked some 12MHz and 16MHz resonators to play with.

The LCD is a 14 pin, 16x4 character LCD from OPTREX. I assume it's compatable with the common Hitachi LCD controller. The only wierd thing about the LCD was that when I used the "move cursor to beginning of x line" commands, the cursor was a couple of spaces off, so I played with it until it looked right.

Here is my code, it's for a 16F628A, using PBP in MPLAB and MPASM

Code:

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' 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      (ground)
'      DB0-3  No connect

    '
    '    PIC Configuration
    '    =================
    '    @ __CONFIG  _INTRC_OSC_NOCLKOUT & _MCLRE_OFF  &  _LVP_OFF & _WDT_OFF & _PWRTE_ON  & _BODEN_ON
 
    @ __CONFIG  _XT_OSC & _MCLRE_OFF  &  _LVP_OFF & _WDT_OFF & _PWRTE_ON  & _BODEN_ON 

    '
    '    Hardware configuration
    '    ======================

        DEFINE OSC 12
    CMCON=7                    ' disable internal comparator
    TRISA=0                    ' Set all PORTA capable i/o to output
    TRISB=0                    ' Set all PORTB i/o to output
   
    '
    '    Hardware initialisation
    '    =======================

DEFINE LCD_LINES 4

    Pause 1000                '1 second for LCD initialisation
    LCDOUT $FE, 1                          ' clear LCD
    '

Start:
    LCDOUT $FE,2,  "    WELCOME    "
    LCDOUT $FE,$C0,"    TO THE    "
    LCDOUT $FE,$90,"  ELECTRICAL  "
    LCDOUT $FE,$D0,"  DEPARTMENT  "


  Pause 3000   


    LCDOUT $FE,2,  "                "
    LCDOUT $FE,$C0,"  Please have  "
    LCDOUT $FE,$90,"  a  seat      "
    LCDOUT $FE,$D0,"                "



  Pause 3000 

    LCDOUT $FE,2,  "  someone will "
    LCDOUT $FE,$C0,"    be  with    "
    LCDOUT $FE,$90,"      you      "
    LCDOUT $FE,$D0,"    shortly    "


  Pause 3000 



    Goto Start

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Thanks for looking.

Look in the PBP manual in the LCDOUT section for commandus and dataus delays and try increasing them a bit.
Also, are you changing your oscillator from XT to HS?

Its working now. That was it. I added this:

DEFINE LCD_COMMANDUS 2000
DEFINE LCD_DATAUS 100

thank you so much, this forum is so helpful.

...yeah, I had to change XT_osc to HS_osc in order to get my 16MHz resonator to work at all. 12MHz seems to be ok with just XT_osc. Is there a frequency where you should start to use HS_osc?

thanks again.

Quote:

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Originally Posted by Max Power

...yeah, I had to change XT_osc to HS_osc in order to get my 16MHz resonator to work at all. 12MHz seems to be ok with just XT_osc. Is there a frequency where you should start to use HS_osc?

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It's in the datasheets for your particular PIC.