Re: HPIB bus commands

From: Nicolas Welte (
Date: 2004-04-13 19:14:19

Hi Larry,

I assume the commands you need to send are single byte commands only. In this 
case, you can make use of the "send secondary" ROM code, which sends bytes 
under ATN control onto the bus, very probably after addressing the device. 
Normally this byte is in a certain range, with the higher bits selecting a 
CBM command (e.g. open or close) and the lower bytes being the actual 
secondary address. I think bytes in the range $00-$1f are not used in the CBM 
syntax, but they are used for standard GPIB messages. Still it should be 
possible to make the CBM ROM send those bytes. If this is what you want, I 
can try to find a ROM entry that you can use. Do you prefer BASIC 2 or BASIC 
4 for programming? For some reason I know that you have available both in 
your PET ;)

I didn't do measurement device programming for quite a while, but I think I 
remember that commands like e.g. unlock can also be sent as a text command 
without ATN. But maybe I'm wrong.


Larry Mollica wrote:
> Hi all. I'm wondering if anyone has experience with, or knows of a source of
> information regarding using the PET to control Hewlett Packard test equipment.
> I need a way to send specific "bus commands" to the HP gear.
>>From what I gather, bus commands are essentially like sending regular data
> except that the ATN line is held low. If there's a way to do this within PET
> basic, it has escaped me.
> I'm thinking that it should be possible to brute-force bus commands by POKEingto
> the PIA such that it simulates sending data with ATN low. It could probably
> cheat some steps too, like using a timing loop rather than looking for proper
> bus hand shakes, etc. There are only a few bus commands I need to send, mostly
> to release control of the instrument front panel.
> I'm hoping someone has already figured this out and knows how to do it...
> Thanks,
> Larry
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