Connect an 18M2's output with another 18M2's input

[Manel_s4]

So I have to link an 18M2's output with another 18M2's inputs as it's drawn in the following image.

I want to know if I must connect this resistor, and if it's right, which resistor must I connect?

Thank you

 

[hippy]

The best way I'd recommend is as attached. The pull-down shown may need to be a pull-up but that will depend on how your program signals from one PICAXE to the others.

 

[Manel_s4]

This is for synchronize the microcontrollers. Which are the resistor's values? I suppose that the three resistors are equal, isn't it?

 

[hippy]

I would likely use 10K resistors myself, but anything from 1K to 20K is likely to be acceptable and probably a wider range than that.

 

[Manel_s4]

I would likely use 10K resistors myself, but anything from 1K to 20K is likely to be acceptable and probably a wider range than that.

Thanks hippy.

 

[inglewoodpete]

Unless you can manage to get the output into an open collector or open drain type configuration (unlikely) or the source PICAXE is to be disconnected, a pullup or pulldown resistor is not required.

The series resistors only have to limit the current if one of the inputs on the slave chips is accidently turned into an output, so do not need to be very large (I would use 1k).

 

[hippy]

The main reason for a pull-up or pull-down is if the output pin is actually a input pin when the PICAXE resets or is downloaded into. This keeps the input pins seeing the 'non active state' until the outputting device has initialised itself. It's not always necessary but won't do any harm in including it.

 

[inglewoodpete]

I have to concede that the pullup/pulldown resistor would make the circuit bulletproof.

However, my choice would still be to use a software solution over a hardware one when issue being resolved cannot damage the hardware. Adding a small initialisation delay in the code for the slave PICAXEs wins for me, over the hassle of mounting another resistor.