What is the D/C pin on the 1.8" TFT LCD breakout?

[xenoc]

Hi there,

I'm trying to understand how the wiring for the 1.8" TFT LCD breakout works, and the D/C pin is confusing me greatly.

My understanding of SPI is that you need the clock (SCK), a data pin for the Arduino to send data (MOSI), a data pin for the Arduino to receive data (MISO), and a chip-select pin for each peripheral (TFT_CS and CARD_CS).

Given that, I'm really confused what the D/C pin on the breakout board is for.

I notice that Adafruit's Micro SD breakout board has CLK, DO, DI, CS pins, which maps fine to my understanding of SPI. So what I'm wondering is if the D/C pin is actually a MOSI pin for the TFT, to keep it separate from the SD card's MOSI pin, for some reason? If that's the case, is there any reason they couldn't both be tied to the same pin on the Arduino?

[adafruit_support_bill]

That is a data/command pin. SPI has no formal standard and there are lots variations on it. Instead of separate CS pins for data and command, they use one CS pin and the D/C to toggle between them.

[xenoc]

Interesting. By this, do you mean that for the LCD controller, the MOSI pin is used for receiving data and commands, and that D/C is set by the master to indicate which it is being sent?

[adafruit_support_bill]

That is right.