TTL level only 1.3V out of 8255 port A

[jcrooke]

I am using a PCI-6025E to do time critical triggering of various devices in my measurement system. I am using handshaked output using the 8255 ports. The voltage level for the the high state is 1.3V. This does not reliably trigger by NI PCI-1411 frame grabber board. If I use a function generator with a 4V high, it triggers every time. Note: I have checked the trigger signal out of my PCI-6025E and it looks good except for the low voltage. My question is this: "Is the high state from the 8255 ports supposed to be so low?"

[jcrooke]

The problem was that I was measuring the voltage across a 50ohm impedance on my oscilloscope. When I switched to 1Mohm, it the voltage went up to 5V, as expected.