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Topics - LBMoelca

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Graphic LCDs / C128128BZ-FSW-GBW and SPI 3-wire
« on: October 14, 2015, 10:31:00 AM »
Good day,

we've purchased your C128128BZ-FSW-GBW display and we are trying to interface it with our SOM using the 3-wire SPI mode. We are facing some problems though.

The first thing we need to clarify is about a statement we found on your site (here):
SPI (3 wire) uses Serial Data Out, Serial Data In, and Serial Clock
SPI (4 wire) adds Chip Select
In the display datasheet is written that the only difference between 3 and 4 wire interface is the presence of the A0 pin, which is used to distinguish data bytes from command ones in 4-wire, without mentioning the CSB. We gave the datasheet priority, so we worked as if CSB was present in 3-wire mode, but since we can't make it work, we were wondering if that sentence may have some relevance to our case. Can you clarify on this?
Anyway, we tried implementing the 4-wire communication, checked that the A0 pin was set to high while sending display data, but still we got nothing on the display.

The second question regards the bytes sent through SPI communication: for display data, in 3-wire mode it seems pretty obvious that we can send more than one byte at a time, since we must specify how many bytes we are sending; for command data, that is pretty unclear. The code examples we found seem to send this data one byte at a time, but none of them covers the 3-wire interface: either way, we didn't find any confirmation that we can send more than one byte at a time, so we tried both ways. Still, no data shown on the display. Is it mandatory then to send one byte at a time, or is there a maximum number of bytes that can be sent?
Just to be clear, when I say "one byte at a time" I mean: "CSB down, one byte sent, CSB up, CSB down, one byte sent, etc", as opposed to "CSB down, N bytes sent, CSB up"

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