What do I connect the load pin to when using SPI?


I am messing with a display module in the link below:

Lascar DDM 4

I am new to SPI and am trying to learn as I go. I am trying to connect the display directly to an Arduino Uno. I do not know where to connect the Load pin or what the load pin does. When I try to google it, I only get information on how to connect the standard SPI pins like MISO, MISO, and Clock. Is the load pin just MOSI? Could someone please explain this to me?


I think by "Load", you mean Chip Select - "CS". That is the fourth, the pin that you have to specify in your code to select the particular SPI device.

So looking the Arduino SPI page below, the pin I would use is pin 10?


So looking the Arduino SPI page, the pin I would use is pin 10?

To match the code.

Lascar linked the datasheet: https://www.lascarelectronics.com/media/2256/ddm-4.pdf

Data is clocked into the internal shift register (DI) on the falling edge of the clock (CK).After 32 bits have been clocked in, setting Load to Logic 1 will cause the contents of the register to be displayed on the LCD.If Load is kept at Logic 1, then the shift register becomes transparent. Any new data that is clocked in will be immediately reflected on the display.

Lazy solution: Tie LOAD to VPOS.

You probably can try the example code for shiftout and use LOAD as latch.

Control the load pin with digitalWrite in the sketch, Do NOT tie high as the load pin is used to sync the data start and end. If you tie the load pin high then garbage will probably get shifted in at power up and the display will lose track of which bit is bit 0.

Pseudo code:

drive load high in setup, data pin low and clock low.
To update display:
drive load low
clock out 32 bits - could use shiftOut but you must call 4 times (8 bits per digit)
drive load high to update the display

Study the data sheet, there will be a mapping between the 7 segments + 1 decimal point with the 8 bits that are shifted out.

Edit: Make sure you do not clock out data too fast, I suggest 1MHz max if you are going to use SPI. If using SPI use Mode 1 as data is the clocked on falling edge.