LCD via 74HC595

**helloo** · - 20th October 2010, 12:22

Hello coders,
I'm stuck in a problem: I've connected a LC display with a 16F876A via a 74HC595 stack IC. But the display does'nt do what I want it to.
The cirquit is O.K., the communication to the stack works fine. And the communication to the display works also fine.
If I try to send the regular initialisation sequence, like there are code examples all over the net, it won't work. So what I did was sending a incrementing byte starting at zero. Code is something like this:

Code:

RS_state = 0

main:      ' 74HC595 : 5=6(E), 4=4(RS), 3=14(DB7), 2=13(DB6), 1=12(DB5), 0=11(DB4)

for char = 0 to 255
gosub tolcd

'pause 500
toggle led

next

goto main

' shiftout datapin,clockpin,msbfirst,[var1, var2]   ' MSBFIRST = 1

sendHalfnibble:
Tosend = char >> 4                          ' High Nibble only, needed for the initialisation routine, move Char 4 bits to the right
gosub sendtolcd  
return

ToLCD:
Tosend = char >> 4                           ' High Nibble, move Char 4 digits to the right
gosub sendtolcd     
tosend = char                                ' Low nibble = char, the other bit's won't matter
gosub sendtolcd                                    
return

SendToLCD:
tosend.4 = RS_state                         ' RS state setzen "0" = command für LCD, "1" = Zeichen an LCD
tosend.5 = 0                                ' Enable Bit OFF                        
shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
high latchpin                               ' write into paralell buffer
low latchpin
'pause 250
 
tosend.5 = 1                                ' enable bit ON
shiftout datapin,clockpin,msbfirst,[tosend]   ' data to HC595
high latchpin                               ' sent to paralell buffer
low latchpin
'pause 250

tosend.5 = 0                                ' Enable OFF
shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
high latchpin                               ' write to paralell
low latchpin
pause 500

return

As you see, the RS pin is always low, wich means there are only commands to the LCD.

What happens with this code is, that the LCD cursor is switching on and off, and moving around at some bytes, wich makes me sure that the cirquit works, but I don't know how to send the high and low nibbles correctly. Everything works, but I don't know why or how, wich gives me a headache.

The stack is connected like: Porta.0 -> clck, Porta.1 -> data, Porta.2 -> latch
porta.3 at the PIC is a LED for debug blinking stuff (to check if the code is still running)

the LCD is connected to the stack like described in the code example (first line)

I've connected a LED to every PIN of the LCD, so with some pauses I can see clearly the data sent to the LCD. This data seems to be O.K. too.

Well so much for that. Now my questions:

A byte within the PIC is bitwise like that: 76543210 wich means bit 7 is the first one, bit zero the last one. What about the nibbles? Are the bits 7654 the high nibble, or bits 3210?

Is it neccesary to send the data first with enable OFF, then with enable ON, then again with enable OFF?

THX for help, and pls excuse my bad english,
helloo

**Darrel Taylor** · - 20th October 2010, 21:08

You were getting close, but it did need a bit more.
The pins I used are probably different than yours.

Code:

INCLUDE "ModeDefs.bas"
INCLUDE "AllDigital.pbp"

datapin    VAR PORTB.1
clockpin   VAR PORTB.0
latchpin   VAR PORTB.2
led        VAR PORTA.5

Tosend     VAR BYTE
char       VAR BYTE
RS_state   VAR BIT



GOSUB InitLCD

main:      ' 74HC595 : 5=6(E), 4=4(RS), 3=14(DB7), 2=13(DB6), 1=12(DB5), 0=11(DB4)

    for char = 32 to 90
        gosub SendData
        pause 500
        toggle led
    next char

goto main

;----[Initialize LCD]----------------------------------------------------------
InitLCD:
    RS_state = 0
    char = $30
    GOSUB sendHalfnibble
    PAUSE 6
    GOSUB sendHalfnibble
    PAUSE 1
    GOSUB sendHalfnibble
    PAUSE 1
    char = $20               ; Start 4-bit mode
    GOSUB sendHalfnibble
    char = $28               ; Function Set, 4-bit, 2-line, 5x7
    GOSUB SendCommand
    char = $0C               ; Display ON
    GOSUB SendCommand
    char = $01               ; Clear Screen
    GOSUB SendCommand
    char = $06               ; Entry Mode
    GOSUB SendCommand
RETURN

;----[Send the Upper nibble to the LCD]----------------------------------------
sendHalfnibble:
    Tosend = char >> 4  ' High Nibble only, needed for the initialisation routine, move Char 4 bits to the right
    GOTO sendtolcd
return

SendCommand:
    RS_state = 0
    GOSUB ToLCD
    PAUSE 2
RETURN

SendData:
    RS_state = 1

ToLCD:
    Tosend = char >> 4                           ' High Nibble, move Char 4 digits to the right
    gosub sendtolcd
    tosend = char & $0F                               ' Low nibble = char, the other bit's won't matter
    gosub sendtolcd
return

SendToLCD:
    tosend.4 = RS_state                         ' RS state setzen "0" = command für LCD, "1" = Zeichen an LCD
    tosend.5 = 0                                ' Enable Bit OFF
    shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
    high latchpin                               ' write into paralell buffer
    low latchpin

    tosend.5 = 1                                ' enable bit ON
    shiftout datapin,clockpin,msbfirst,[tosend]   ' data to HC595
    high latchpin                               ' sent to paralell buffer
    low latchpin

    tosend.5 = 0                                ' Enable OFF
    shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
    high latchpin                               ' write to paralell
    low latchpin
    pauseus 50
return

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**helloo** · - 24th October 2010, 14:13

Hi Darryl,
thank you for trying to help, but after another three days of trying, changing bytes, switching bits, I am pretty sure that my LCD doesnt meet HD44780 specs for 100%.

Your code does exact the same as mine did before.

So I managed somehow to print out some chars, wich makes me sure:
1. the LCD switches to 4 bit mode
2. the wiring is right

but I could'nt use the 2nd line, nor some other commands.

the next thing I tried was to connect the LC display directly to the pic without the stack - just the same.

and then I tried to write stuff with the LCDOUT command - nothing.

Now I ordered some other LCD's wich are used by other people before (LCD1602). Next week I'll see what happenes.

Again, thanks.

**sayzer** · - 26th October 2010, 15:34

Originally Posted by Darrel Taylor

You were getting close, but it did need a bit more.
The pins I used are probably different than yours.

Code:

INCLUDE "ModeDefs.bas"
INCLUDE "AllDigital.pbp"

datapin    VAR PORTB.1
clockpin   VAR PORTB.0
latchpin   VAR PORTB.2
led        VAR PORTA.5

Tosend     VAR BYTE
char       VAR BYTE
RS_state   VAR BIT



GOSUB InitLCD

main:      ' 74HC595 : 5=6(E), 4=4(RS), 3=14(DB7), 2=13(DB6), 1=12(DB5), 0=11(DB4)

    for char = 32 to 90
        gosub SendData
        pause 500
        toggle led
    next char

goto main

;----[Initialize LCD]----------------------------------------------------------
InitLCD:
    RS_state = 0
    char = $30
    GOSUB sendHalfnibble
    PAUSE 6
    GOSUB sendHalfnibble
    PAUSE 1
    GOSUB sendHalfnibble
    PAUSE 1
    char = $20               ; Start 4-bit mode
    GOSUB sendHalfnibble
    char = $28               ; Function Set, 4-bit, 2-line, 5x7
    GOSUB SendCommand
    char = $0C               ; Display ON
    GOSUB SendCommand
    char = $01               ; Clear Screen
    GOSUB SendCommand
    char = $06               ; Entry Mode
    GOSUB SendCommand
RETURN

;----[Send the Upper nibble to the LCD]----------------------------------------
sendHalfnibble:
    Tosend = char >> 4  ' High Nibble only, needed for the initialisation routine, move Char 4 bits to the right
    GOTO sendtolcd
return

SendCommand:
    RS_state = 0
    GOSUB ToLCD
    PAUSE 2
RETURN

SendData:
    RS_state = 1

ToLCD:
    Tosend = char >> 4                           ' High Nibble, move Char 4 digits to the right
    gosub sendtolcd
    tosend = char & $0F                               ' Low nibble = char, the other bit's won't matter
    gosub sendtolcd
return

SendToLCD:
    tosend.4 = RS_state                         ' RS state setzen "0" = command für LCD, "1" = Zeichen an LCD
    tosend.5 = 0                                ' Enable Bit OFF
    shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
    high latchpin                               ' write into paralell buffer
    low latchpin

    tosend.5 = 1                                ' enable bit ON
    shiftout datapin,clockpin,msbfirst,[tosend]   ' data to HC595
    high latchpin                               ' sent to paralell buffer
    low latchpin

    tosend.5 = 0                                ' Enable OFF
    shiftout datapin,clockpin,msbfirst,[tosend]   ' send data to HC595
    high latchpin                               ' write to paralell
    low latchpin
    pauseus 50
return

Attachment 4867

Darrel,

Would that be possible to use 595_LCD routine (above) with a Hijacked LCDOUT command?

Something like your LCDAnypin hijacking.

________

**Darrel Taylor** · - 26th October 2010, 16:20

Originally Posted by sayzer

Would that be possible to use 595_LCD routine (above) with a Hijacked LCDOUT command?
Something like your LCDAnypin hijacking.

Yes it would ... with some modification.

But you may want to check out this post from Guido which uses a 74xx164 shift register and only uses 2 pins on the PIC with the HighJack routines.

http://www.picbasic.co.uk/forum/show...5344#post95344

**helloo** · - 28th October 2010, 19:48

Hi coders,
yepp, it was the darn LC display. I tried the 1602, and the code works. *grnnpgf* I spent 5 days of trying for nothing...

Anyway, the next goal is to store strings in PICs memory, and shift them out to the LCD. Darryls "STRINGS.PBP" looks very interesting. I think I use his routines again...

I'll write again.

**sayzer** · - 29th October 2010, 08:17

Originally Posted by Darrel Taylor

Yes it would ... with some modification.

But you may want to check out this post from Guido which uses a 74xx164 shift register and only uses 2 pins on the PIC with the HighJack routines.

http://www.picbasic.co.uk/forum/show...5344#post95344

Thank you Darrel.
Guido's way did not work in my simulator. I will make the real circuit assuming that the simulator could not simulate it.

**helloo** · - 31st October 2010, 20:49

The circuit and the program work now. It's easily possible to drive up to three LCDs with only three I/O pins of the µC. Darryls "strings.pbp" work with only minor changes for my program. Thanks again, Darryl.

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