3 replies to this topic

[bill.french]

Form the manual for my uLCD-144: (emphasis mine)

Master Reset signal. Internally pulled up to 3.3V via a 4.7K resistor. An
active Low pulse greater than 2 micro-seconds will reset the module. If
the module needs to be reset externally, only use open collector type
circuits. This pin is not driven low by any internal conditions. The host
should control this pin via one of its port pins using an open
collector/drain arrangement.

From wikipedia, I feel like I have a good handle on what "open collector" means -- but how do I do that with a netduino?

[Mark H]

Exactly as the circuit in the wikipedia article shows.



Connect IC Ouput to one of the pins on your netduino, IC ground to the GND pin on the netduino, and "Open" collector to the reset pin on your LCD.




Then to reset, set your Digital output to true for more than 2us (a 1ms Thread.Sleep is heaps of time) and that will pull the reset pin to ground.

[Fred]

You forgot a resistor between the Netduino pin and the base of the transistor in the diagram above. There will also be the issue that the netduino pin will float high as it boots up and will reset the external device. Personally, I'd try connecting the Netduino directly. It does have an internal pull-up resistor to 3.3V, but I suspect this won't make any difference. The warning probably relates to connecting something (maybe an Arduino) that pulls up to another voltage like 5V.

[bill.french]

Great, thanks for the feedback. I wasn't sure if with the netduino I could set it to an inputport and get the same open collector effect -- or use some other technique in code that does not require a transistor (and resistor as fred stated!) Right now I have it hooked up directly to the netduino and it works fine. So....