piclist 2001\11\08\140606a >
Thread: LCD panel init problems
face BY : Wollenberg, Frank email (remove spam text)

In response to Quentin [spamBeGoneqscTakeThisOuTspamICON.CO.ZA]

> Your 4 bit data line is connected to the 4 MSB data lines of the LCD.
> The other 4 LSB of the LCD is tied to gnd.

> So, when you put the MSB of b'0011' on the LCD there is
> already b'0000'
> on the 4 LSB of the LCD (connected to gnd)
> So in actual fact you are sending 8 bit data.
> Sending b'0011' and the LCD thinks you are actually sending
> b'00110000'
> After you did this 3 times, you tell the LCD, OK, now we are going to
> use 4 bit comms.
Right, also. But you mean the init sequence after power-up of the LCD.

What i have described is the following situation:
 1. the uP and the LCD has been powered up correctly
 2. the LCD has been initialized by the uP into the 4-bit mode (as you have
 3. the uP starts sending a command to the LCD, which is 8bit wide, send in
2 chunks of 4bit.
 4. after the first chunk only! the uP is reset (brown-out, ESD or what
 5. the uP restarts
 6. the uP sends the init sequence (as in item 2)

The LCD doesn't know of the uP-reset. The LCD is getting any 4bit data,
which it must interpret in some (the correct) way. Because the LCD is in
4bit mode, it expects two 4bit chunks.


GSP Sprachtechnologie GmbH
Frank Wollenberg
Tel.:   +49 (0)30 769929-78
Fax:    +49 (0)30 769929-12
eMail:  .....f.wollenbergspamspamgsp-berlin.de

GSP Sprachtechnologie GmbH
Teltowkanalstr.1, D-12247 Berlin
Tel.:  +49 (0)30 769929-0
Fax:   +49 (0)30 769929-12
eMail: RemoveMEInfospamspamEraseMEgsp-berlin.de
Web:   http://www.gsp-berlin.de

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See also: www.piclist.com/techref/lcds.htm?key=lcd
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