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'[PIC]: LCD 4bit or 7bit?'
2003\05\10@063220 by Tal

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Hi

Can you explain what are the differences between the 4bit & 7bit regarding
LCD displays?
are they any differences at all? any limitations? when I should use 4bit or
7bit?

Regards

Tal

"I have not failed. I've just found 10,000 ways that won't work."
Thomas Edison

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2003\05\10@064504 by Tan Chun Chiek

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i assume you are talking about communicating thru a 4bit or 8bit bus to a
HD44780 lcd.

Pros of 4bit comms: only 7 I/O lines needed to interface.
Cons of 4bit comms: slightly more code required to drive the display

Pros and cons of 8bit comms being directly the opposite of 4bit, with 8bit
needing 13 I/Os

Regards,
Chun Chiek

{Original Message removed}

2003\05\10@065344 by Tal

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yes you are right sorry i mean 8 bit.
10x for help.

Tal

-----Original Message-----
From: pic microcontroller discussion list
[.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On Behalf Of Tan Chun Chiek
Sent: Saturday, May 10, 2003 1:43 PM
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: Re: [PIC]: LCD 4bit or 7bit?


i assume you are talking about communicating thru a 4bit or 8bit bus to a
HD44780 lcd.

Pros of 4bit comms: only 7 I/O lines needed to interface.
Cons of 4bit comms: slightly more code required to drive the display

Pros and cons of 8bit comms being directly the opposite of 4bit, with 8bit
needing 13 I/Os

Regards,
Chun Chiek

----- Original Message -----
From: "Tal" <.....kooterKILLspamspam.....012.NET.IL>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Saturday, May 10, 2003 6:31 PM
Subject: [PIC]: LCD 4bit or 7bit?


> Hi
>
> Can you explain what are the differences between the 4bit & 7bit regarding
> LCD displays?
> are they any differences at all? any limitations? when I should use 4bit
or
{Quote hidden}

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2003\05\10@065355 by Jinx

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> Can you explain what are the differences between the 4bit & 7bit
> regarding LCD displays?
> are they any differences at all? any limitations? when I should use
> 4bit or 7bit?
>
> Regards
>
> Tal

You mean 4-bit or 8-bit ?

No functional difference but s/w is (slightly) more complex and it
does take longer because you have two 4-bit nybbles to transfer
instead of one 8-bit byte. 4-bit uses fewer port pins of course,
which may be an important consideration

Funny you ask - I'm actually right in the very middle of doing some
code for a 4-bit LCD. The data lines will be the top half of an F628
PortB so I can freely use INT0 and the UART, both in the lower half

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2003\05\10@065552 by Kyrre Aalerud

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Yep...

The extra code would be to clock out first 4 bits of the data/command then
swap the nibbles and send the 4 remaining.  It does take twice as long to
send a single char though, as one has to observe the timing requirements of
the display.

   KreAture

{Original Message removed}

2003\05\10@081230 by Oliver Broad

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Normally on a PIC project you would chose 4 bit to minimise the number of
pins required, almost always.

8 bit mode is best used if you happen to already have an 8 bit wide bus that
the display can hang off of. Remember that the data lines, RS and R/W (if
used) can be shared with other peripherals, only "E" needs to be exclusive.
8 bit mode might be used if you happen to have a lot of I/O pins spare
8 bit mode might be used for speed if the PIC clock frequency is extremely
low
8 bit mode might be used if you are controlling the display serally via
shift registers and you want to minimise the number of operations required
8 bit mode might be advisable for a LCD "newbie" since it has the best
chance of working first time.


{Original Message removed}

2003\05\10@105741 by Tal

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Thanks all for sharing your ideas/knowledge

Tal

-----Original Message-----
From: pic microcontroller discussion list
[spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU]On Behalf Of Oliver Broad
Sent: Saturday, May 10, 2003 3:15 PM
To: TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU
Subject: Re: [PIC]: LCD 4bit or 7bit?


Normally on a PIC project you would chose 4 bit to minimise the number of
pins required, almost always.

8 bit mode is best used if you happen to already have an 8 bit wide bus that
the display can hang off of. Remember that the data lines, RS and R/W (if
used) can be shared with other peripherals, only "E" needs to be exclusive.
8 bit mode might be used if you happen to have a lot of I/O pins spare
8 bit mode might be used for speed if the PIC clock frequency is extremely
low
8 bit mode might be used if you are controlling the display serally via
shift registers and you want to minimise the number of operations required
8 bit mode might be advisable for a LCD "newbie" since it has the best
chance of working first time.


----- Original Message -----
From: "Tal" <RemoveMEkooterspamTakeThisOuT012.NET.IL>
To: <PICLISTEraseMEspam.....MITVMA.MIT.EDU>
Sent: 10 May 2003 11:31
Subject: [PIC]: LCD 4bit or 7bit?


> Hi
>
> Can you explain what are the differences between the 4bit & 7bit regarding
> LCD displays?
> are they any differences at all? any limitations? when I should use 4bit
or
{Quote hidden}

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2003\05\10@132611 by Mike Harrison

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On Sat, 10 May 2003 13:06:46 +0200, you wrote:

>Yep...
>
>The extra code would be to clock out first 4 bits of the data/command then
>swap the nibbles and send the 4 remaining.  It does take twice as long to
>send a single char though, as one has to observe the timing requirements of
>the display.
I don't believe any significant delay is required between nibbles though (compared to the command
execution time required for eac byte) , so the time the LCD takes to process each byte is much
longer than the extra time to send 2 nibbles in 4 bit mode.
The only reason I can think that you would ever want to use 8 bit mode is when running a very slow
PIC clock (e.g. 32K watch crystal).

I suspect 8 bit mode was only ever put there in the first place  to allow displays to be generated
by hardware withoyt a processor - e.g. EPROMS. Remember these controllers date back to when CPUs
were an awful lot more expensive than PICs are.

>    KreAture
>
>{Original Message removed}

2003\05\10@170719 by Kyrre Aalerud

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True true...

I prefer the I2C or other serial bus based ones.
They allow for a minimal use of I/O's

   KreAture

{Original Message removed}

2003\05\10@171400 by Bob Ammerman

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> I suspect 8 bit mode was only ever put there in the first place  to allow
displays to be generated
> by hardware withoyt a processor - e.g. EPROMS. Remember these controllers
date back to when CPUs
> were an awful lot more expensive than PICs are.

Actually, the 8-bit bus fit very well with many microprocessors (not
microcontrollers!) of the time: 8080, Z80, 6800, 6502, etc.

Bob Ammerman
RAm Systems


>    KreAture
>
>{Original Message removed}

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