DS133: jumper on INTA & INTB to arduino

Using Arduino Project Guidance
1

I am building a shield for an arduino UNO that contains a DS1337+. The schematics below is a [very] simplified version:


(several components, like crystal, omitted for brevity)

U1 is the arduino shield itself, with pins directly connecting to the arduino UNO.

What I am planning is to have 2 jumpers connecting - or not - the DS1337's INTA and INTB to the arduino's interrupt ports (D2 and D3). According to the DS1337 datasheet, the INTA and INTB ports are open drain outputs, and require and external pullup resistor. Thus my questions:

  1. What are the good values for the pullup resistors?

  2. Is it possible to use a single resistor for both ports or does each one need its own resistor?

  3. JMP1 is the jumper (they will be pin headers, not dip switches) that will either enable or disable the use of the interrupts but the arduino, because another shield might require those 2 ports on the arduino. If JMP1 has both lines open, the INTA and INTB ports in the DS1337 wiill be getting some voltage from the arduino. Is that ok? Can these 2 ports receive the voltage without being connected to anything else?

Thanks in advance.

2
  1. What are the good values for the pullup resistors?

The datasheet says that the outputs can sink 3 mA. 2K at 5V would be 2.5 mA so that would be a good minimum. Anything between there and 10K should be good.

  1. Is it possible to use a single resistor for both ports or does each one need its own resistor?

If you connect the outputs together you will get a logical OR of the two signals (the signal will go low if either output goes low). If that is what you want then you can use a single resistor for both.

  1. If JMP1 has both lines open, the INTA and INTB ports in the DS1337 wiill be getting some voltage from the arduino. Is that ok?

Yes. The chip doesn't care much if the outputs are used or not. It's just turning on a switch that connects the output to Ground. As long as you don't shove more than 3 mA into the outputs they will be fine.

3

Thank you very much, John!

As long as you don't shove more than 3 mA into the outputs they will be fine.

In that case, I think I'l replace the resistors for something like 4k7, just to make sure I am not near the upper limit of the allowed current for the gates.

Once again thanks.