|Re: HP-IL: Using 82162A Printer and PIL-Box in Same Loop|
Message #2 Posted by Howard Owen on 16 May 2012, 2:53 a.m.,
in response to message #1 by Les Wright
When the calculator (or other controller) sets up the loop, it assigns numerical addresses to each device according to where they sit in the loop physically. The first device encountered in the direction that data flows around the loop is given a loop address of 1. The next one gets 2 and so on until all the devices are enumerated. The device with loop address 1 is designated the "primary" device.
Here's what occurs when you use the loop with the default AUTOIO mode set. If you try to print something, the interface will start at the primary device looking for a printer. (It looks for a device ID with the right numeric value for a printer.) The first one it finds gets the print job. The same thing happens with mass storage commands - the first disk-like device gets the data. You can select other devices by changing the calculator's idea of the primary device. If the 1st and 4th devices in the loop are printers, and you want to print to the one with address 4, you could execute AUTOIO, 4, SELECT. (The initial AUTOIO isn't needed if you are already in that mode, as you are by default.) After these commands, the calculator will start its search at device 4, and will find your desired printer first. You could also SELECT device 2 or 3 and it would have the same effect - your printer would be found first before the one at address 1.
So your calculator must be connected to the PIL-Box in such a way that its virtual devices are first in the loop from the HP-41's point of view. You could re-cable so that your printer was the first device the 41 sees. The male plug on the interface is the one that data will flow towards. But it's also easy to just 3 SELECT to skip the first two virtual devices when searching for the printer.
I think the museum DVD has the HP-IL interface manual. It should be called "HP82160A HPIL Module.pdf". I drew the above information from chapter 4, beginning on page 43, and especially page 46, which discusses SELECT. If you can't find it, drop me some mail, and I'll send you a copy.
Hope this helps.