I have an HP75C and an HP3421A Data Aquisition Unit. I have been able to talk to the HP3421A and get it to reset and measure DC Volts, but I cannot read the result back into the HP75C.
I think that either the IO ROM or the I/O Utilities will allow me to do this.
Can someone confirm this for me?
If so, is there a way I can hold of these (I currently have a Wanted Ad running on the Ads page).

Thanks for any help,



ENTER D;V should do it, where D is the device address of the 3421, and V is the variable you want to read the voltage into.


Hi Garth - Thanks for the quick reply.

When I try to enter the "ENTER" command I get a syntax error and the cursor points to the "t".

I should mention that I don't have the I/O ROM or Utilities. I am guessing that I need one or the other to make the HP75 recognise the ENTER keyword.

Is this correct?




The 71B has ENTER in the ROM that comes with the HP-IL module. I assume that the 75 has only the mass storage and printer support readily available in its ROM.


What you need are the SENDIO & ENTIO$ commands from the HP-75 I/O Utiliities. The I/O Utilities manual is on the Museum DVD. I sent more details in an e-mail.


Ah yes-- I have an old beat-up 75 here someone gave me, but have never used it. I got the instruction above from the HP-75 section of a 28-page piece of HP literature that tells about using the 3421 with the 71 or 75, and in my quick scan, did not see that it says the 75 needs the I/O ROM (p/n 00075 15001). Like the other post says, the 71 (which I have used extensively, unlike the 75) doesn't need any extra modules because it has everything in its HPIL module.


Hi Everyone,

Thanks for the information. I understand that the easiest is to get the I/O Utilities as the I/O ROM is quite hard to find for the 75.

I will chase the I/O Utilities, but not give up on the I/O ROM just in case one turns up.

I am just starting to chase up the bits I need to get my system up and running so will be looking out for other HP-IL devices (eg an HP-IL to RS232 converter) as well since I want to send the data to a PC for logging and analysis. I tend to collect stuff, so may get other bits as well.

Thanks to everyone for their help.


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