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sema_tufan
Joined: 03 Mar 2020 Posts: 14 Location: turkey
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Ttelmah
Joined: 11 Mar 2010 Posts: 19504
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Posted: Mon Jun 28, 2021 7:57 am |
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People have worked on this in the past:
[url]
https://ccsinfo.com/forum/viewtopic.php?p=176258
[/url]
However the huge 'caveat' is the very last comment in the thread. This is
a 3.3v chip. It is not suitable for direct drive off a 5v PIC without level
shifting.
The experiments probably didn't work because of this,,, |
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Jerson
Joined: 31 Jul 2009 Posts: 125 Location: Bombay, India
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Posted: Tue Jun 29, 2021 8:31 pm |
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The specific display shown by the OP will work on 5V. This is the Arduino UNO shield. |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19504
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Posted: Tue Jun 29, 2021 11:30 pm |
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You have to be very careful about this.
The Arduino, has TTL type inputs. The PIC (on SPI), has Schmidt inputs.
So an 'Arduino shield' for such a device, should have 5v to 3.3v translation
on the output pins, but will rely on the existing Arduino inputs being able
to accept the 3.3v output from the device.
The PIC though will not accept these same signals, without:
A 3.3v PIC
Or using software SPI on pins that accept TTL inputs
Or using hardware level shifters.
It's a big 'caveat'.... |
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temtronic
Joined: 01 Jul 2010 Posts: 9225 Location: Greensville,Ontario
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Posted: Thu Jul 01, 2021 8:48 am |
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Since most of the peripherals/modules made today are usually 3 volt devices, it makes sense to use a 3 volt PIC.
It allows for direct pin to pin connecting, so easier and cheaper.
There are PICs, like the 18F46K22, that will run at 3 or 5 volts, most 'L' version PICs only run at a lower voltage. So check the datasheets ! |
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Jerson
Joined: 31 Jul 2009 Posts: 125 Location: Bombay, India
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Posted: Thu Jul 01, 2021 9:37 pm |
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I have successfully used such 'display shields' in my ARM CM0 projects @5V. The level shifters on the shield take care of voltage translations between 3.3 and 5V. So, I am quite confident it should work on PIC too though I do not have first hand experience on PIC to claim so. |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19504
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Posted: Fri Jul 02, 2021 12:34 am |
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No,
As I explained, the shields have the adapters to translate the 5v ARM signals
to the 3.3v levels the displays use, but they do not have any adapters
on the signals from the display to the ARM. They rely on the fact that the
ARM 5v 'inputs' are TTL compatible inputs (so accept anything above 2.4v
as a logic 1). The 3.3v signals therefore work fine. The problem is that the
PIC SPI input has Schmidt inputs, which require 4v for a logic '1'. The 3.3v
signals don't give this. Result problems.....
This happens with just about all ARM shields, but is only a problem for
things using SPI.
Look at the thread at the top of the forum for interfacing an SD card,
which has a link to a suitable level shifter. |
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