Are Pulldown resistors required for PROP I/O to ULN2803A Device?

DavidM

Hi,

I need to hook up 16 Prop I/O Pins to a ULN2803A Device ( Darling Array ).

I understand that when the PROP chip starts up there is a small period of time ( under half a second??) where all the I/O Pins are FLOATING ( hi Impedance), These 16 I/O pins will be set to OUTPUTS in my INIT CODE, and a LOGIC HI will drive the ULN2803A Device when needed.

So my question is..

Q1) Is it best to pull down by default, each of the 16 I/O Lines to VSS via 10K Resistor?
Q2) Will this prevent "UNWANTED" signals during start up?

Also,

Q3) Is a series resistor required between the PROP I/O pins and the ULN2803A Inputs?


Thanks

Dave M

Ariba

If you look at the details of one darlington channel in the 2803 you see the resitors are already there.


So:
A1) not necessary
A2) The darlington will be switched off while the pin is an input (because of the 7.2k and 3k resistors to Ground)
A3) no there is already a 2.7k series resistor

Andy

DavidM

HI Ariba,

Thanks for the reply, I like your answer as now I don't have to try to fit the resistors in! as I don't have much room!

Looking at the schematic makes sense now, I only briefly looked at it when selecting this device.

Regards