HP-71B won't turn off when loop is broken

[Joe Horn]

Old Titan users: help! My '71B turns off just fine when the HP-IL loop is connected, but when I break the loop (by turning off a device or by unplugging the cable), the '71 turns itself back on immediately after I turn it off. My desire to know why is greater than my shame at not knowing the answer, hence this posting. Thanks in advance for any help you can give me!

[Dave Frederickson]

Can you connect a PIL-Box and run ILPER to sniff the loop? I suspect it has something to do with the Loop Power-Down (LPD) message. See The HP-IL System, p72.

Dave

[RayAtHP]

OFF IO resets DISPLAY IS and PRINTER IS assignments, suspends all IO by Titan on the loop, RESTORE IO is it's counterpart.

RESET HPIL resets Titan's IL device, has no impact on the loop.

CLEAR <Device>| LOOP clears one specific assigned device or the complete loop. Clearing is like a device reset.

Ray

[Sylvain Cote]

Dave's suggestion is interesting.
My take, it's either that or the HP-IL interface internal registers are corrupted or in inconsistent states.
I would at least try Dave suggestion,
then if it's not working reset the interface (RESET HPIL, OFF IO, RESTORE IO)
then if it's still not working completely remove the interface from the 71, power cycle the computer then reinstall the interface.
Sylvain

[J-F Garnier]

This is a common, well-known (at least be me:-) behavior of the HP-71B HP-IL. Nothing is bad in your machine.
A hanged or interrupted HP-IL transfer (when you press ATTN twice and get the "HPIL: Aborted" message) often lead to this situation.
The HP-IL module has still 'something' to say to the Saturn CPU, and this one doesn't want to listen.
RESET HPIL will force the HP-IL module to stay quiet :-)

J-F

For the people interested, it's very easy to reproduce:
Open the loop,
do RESET HPIL, RESTORE IO,
interrupt RESTORE IO with ATTN twice,
try to turn off the HP-71B...
If then you close the loop and retry a RESTORE IO, you will usually get a "HP-IL:Unexpected Message" - the HP-71B received something from the HP-IL module that it didn't expect.

[Joe Horn]

(05-21-2014 01:22 PM)J-F Garnier Wrote:  RESET HPIL will force the HP-IL module to stay quiet :-)

Thanks, J-F, for your explanation and solution! Thanks to Dave, Ray, and Sylvain too for your insights. My '71 no longer has insomnia.

[J-F Garnier]

Apart from the double ATTN keystroke interruption, an other common cause of this behavior is having a "DISPLAY IS :DISPLAY" configuration (this is the default one); with it the HP-71B tries, even if the loop is broken, to communicate on the loop searching for a display, and this can hang the HP-IL module as well.
Doing "DISPLAY IS *" prevents it, when there is no need of an external display.

J-F