[En-Nut-Discussion] ethernut board 3.1 LCD support

[Paul Govers]

Hello Ulrich,

thank you for your reply, its very clear for me now!
i choose for the option to not polling the Busy-Flag and leave my cannon at
home :-)
and i will put some time in how to configure the CPLD, i never done it.

Greetings 
Paul


uprinz wrote:
> 
> Hi!
> 
> You can go two ways:
> 
> Use the display out of the box and if it is a 5V display, use one of 
> TI's SN74AVCxxx series buffers for level adaption. But with EN3 the 
> simplest way is to use the CPLD and configure it for routing some 
> signals straight through, from input to output.
> 
> Second way is to find the 91k resistor on the displays PCB and replace 
> it with a 75kR type. Then the display can be driven with 3.3V. In worst 
> case you need to generate a slight negative LCD voltage to get a better 
> contrast.
> 
> I didn't check for the memory setup of the AT91 series. If you can slow 
> down memory access enough and can configure one /CSx line for beeing 
> active-high you cann access the display directly as a memory instead of 
> going gpio way. If there /CS cannot be configured as active high, there 
> is an option to use one of these single-gates 74AVC12xG1 for inverting 
> /CS to E.
> 
> This way of connecting LCDs is only suitable for CPUs having a 
> data/address bus already routed to a connector. It doesn't mace any 
> sense for all other systems.
> 
> There are lots of ways to connect a display...
> 
> I do not think that there is any good reason for polling the Busy-Flag.
> 1) It needs a lot of time as the display thread blocks for the whole 
> time while polling. Other tasks may run out of time.
> 
> 2) If you use NutSleep() to unblock other tasks while waiting, you do 
> not need to poll the display as, besides two commands, all are finished 
> long before the display task is back again. The two commands Clear and 
> Home can be exited with NutSleep(2) instead of NutSleep(1).
> 
> 3) With a charater display there is no need to be fast. With my slowest 
> driver implementation (Using NutSleep(1) after each byte sent to the 
> LCD) an 40x4 LCD is updated completely after approx. 100ms. That are 10 
> complete refreshes in one second!
> 
> Don't chase birds with cannons :)
> 
> Best regards, Ulrich
> 
> Am 12.05.2010 09:12, schrieb Paul Govers:
>> Hi Ulrich,
>>
>> Thats a good reminder that most of the IO is not 5volt tolerant!
>> Iam happy that i yesterday have not read from the Dispay :-)
>> I succeeded to control the display in 4-bit mode, yesterday only one
>> character but the rest would be simple!
>>
>> I will have a look at the CPLD, because i want to read the display to
>> know if the LCD is busy or not and i will take a look at level-shifters
>> IC's
>>
>> Does someone know ready for use/Plug and play level-shifters? (maybe a
>> good product for in the egnite webshop!)
>>
>> --
>>
>> Met vriendelijke groet / with kind regards,
>>
>> Paul Govers
>>
>>
>> -----Original Message-----
>> From: en-nut-discussion-bounces at egnite.de
>> [mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of Ulrich Prinz
>> Sent: Tuesday, May 11, 2010 7:55 PM
>> To: Ethernut User Chat (English)
>> Subject: Re: [En-Nut-Discussion] ethernut board 3.1 LCD support
>>
>> Hi Paul!
>>
>> Am 11.05.2010 10:30, schrieb Paul Govers:
>>>
>>> Hi Ulrich,
>>>
>>> Thats great that you working on an LCD driver for the ethernut 3.1
>> board!
>>> i will try tonight to get my LCD display working with my Ethernut 3.1
>> board,
>>> i have read the documentatie about the HD44780 and it seems not to
>> difficult
>>>
>> I replaced the driver for AT91, it is not specialized on the EN 3.1 but
>> it should work with all AT91 devices.
>> It uses GPIO for all signals and, in this release, will not support
>> reading from the display. And this is something you might want, as the
>> CPU on the EN 3.1 has no 5V tolerant pins. Reading without
>> level-shifters will destroy the CPU if the display is driven with 5V. On
>>
>> the other hand you might use the CPLD as a level shifter, it is 5V
>> tolerant even driven with 3.3V or less.
>>
>> I think I don't have time tonight for checking in my driver, but I will
>> do it tomorrow night for sure. I actually think for adding another
>> access method, the memory interface. I didn't check the data sheets of
>> all AT91 if they can be programmed for such slow memories and if they
>> are able to drive an active-high chip select.
>>
>> Best regards, Ulrich
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