sinking unused pins

[CF_eee]

Hi,

I am only using 8 I/O pins on a pci-6503. I wanted to sink the rest of them to ground through a resistor. Above what value is fine? I was thinking of having a huge one at 1M ohm but someone said that might cause problems too. Help? Thanks in advance.

-Chris

[Travis G.]

Hello Chris,

By default, all lines on the PCI-6503 are pulled up to +5V through a 100 kOhm internal resistor.  There is a jumper on the device labeled W1 that when set to low, will pull all the digital lines to ground through a 100 kOhm resistor rather than pull the lines high.  Changing this jumper is the easiest method for changing the default state of the digital lines on the device.  Take a look at the Digital I/O Power Up State Selection section of the 6503 User Manual for more information.

PCI-DIO-96/PXI-6508/PCI-6503 User Manual

This section also discusses adding external resistors to pull the lines low, and recommends a resistor value of 7.1 kOhms to pull the line low, with the W1 jumper set to pull the line high.  I hope this helps,

Travis G. | Applications Engineering | National Instruments | www.ni.com/support