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PICList Thread
'Hitachi HD44780'
1998\09\02@083345 by Ivan Cenov

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hi,
i have to drive one LCD module with Hitachi HD44780 compatible chip
inside it.
My question is for E (enable) signal.
1. Should it to be continuous (as E (f2) with motorola's 6800, hc11) ?
2. I saw an example for HTsoft C compiler and it seems
that E is driven when read or write is performed only.

What of these cases is true ?

Ivan Cenov
spam_OUTokto7TakeThisOuTspambotev.ttm.bg
www.geocities.com/SiliconValley/Network/9276/
Do what have to do, let happens what it wants.

1998\09\02@090509 by org Hager

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On Wed, 2 Sep 1998, Ivan Cenov wrote:

> hi,
> i have to drive one LCD module with Hitachi HD44780 compatible chip
> inside it.
> My question is for E (enable) signal.
> 1. Should it to be continuous (as E (f2) with motorola's 6800, hc11) ?

No. Depending on the status of the R/W and RS signals, you would get
unwanted read or write operations all the time.

> 2. I saw an example for HTsoft C compiler and it seems
> that E is driven when read or write is performed only.

Yes, that's correct. The data is latched into the controller at the
falling edge of the E signal.

Georg.

1998\09\02@091310 by Chip Weller

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Ivan Cenov wrote:
>hi,
>i have to drive one LCD module with Hitachi HD44780 compatible chip
>inside it.
>My question is for E (enable) signal.
>1. Should it to be continuous (as E (f2) with motorola's 6800, hc11) ?
>2. I saw an example for HTsoft C compiler and it seems
>that E is driven when read or write is performed only.
>
>What of these cases is true ?


#2 is correct. When decoding for a 68HC11 I always AND the E clock with
the LCD select address. E should be a positive going pulse, The address
and direction lines (RS and R/W) need to be set at least 140ns before E
goes high and on writes to the LCD the data needs to be set 195ns before
E goes low (which latches the data). The address and data needs to be
held at least 10ns after E goes low.

On the PIC translates into a minimum of three PORT write operations to
write a byte/nibble to the display, set up data/address, set E, clear E
on to next byte/nibble.

Chip Weller.

1998\09\02@091755 by paulb

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Ivan Cenov wrote:

> i have to drive one LCD module with Hitachi HD44780 compatible chip
> inside it.
> My question is for E (enable) signal.
> 1. Should it to be continuous (as E (f2) with motorola's 6800, hc11) ?
> 2. I saw an example for HTsoft C compiler and it seems
> that E is driven when read or write is performed only.

 Enable in this case, means Chip Select.  If R/W is in Write state,
every such access writes something to the chip.  Take note!
--
 Cheers,
       Paul B.

1998\09\02@094244 by Mike Keitz

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On Wed, 2 Sep 1998 15:19:24 +0300 Ivan Cenov <.....okto7KILLspamspam@spam@BOTEV.TTM.BG> writes:
>hi,
>i have to drive one LCD module with Hitachi HD44780 compatible chip
>inside it.
>My question is for E (enable) signal.
>1. Should it to be continuous (as E (f2) with motorola's 6800, hc11) ?

No, it must be pulsed with each read or write.  It isn't a clock, it's a
chip select.  When the E signal is low, the data on the other pins of the
LCD is don't care, allowing them to be shared with other hardware.  The
original intent was to connect the LCD to a VonNeuman processor's 8-bit
bus.  When E is high, the LCD inputs or outputs.  If you are polling the
status bit to see when the LCD is busy (not recommended for beginners,
put in lots of delay instead), E must pulse low then high in order to
latch a new copy of the busy bit.  If you just hold E high while the LCD
is busy, the data output won't change back to not busy when it is not
busy.

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1998\09\03@012845 by Ivan Cenov

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thanks to Chip Weller, Mike and others who helped.
I hoped that this is the case (easier one).
Ivan Cenov

{Original Message removed}

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