HP1350 Graphics Translators

From: vassilip_at_dsl.cis.upenn.edu <(vassilip_at_dsl.cis.upenn.edu)>
Date: Sat Jun 21 18:06:00 2003

Bob Shannon <bshannon_at_tiac.net> in cctalk-647 wrote:
> As long at I have the HP bus analyzer connected, and set for SLOW or
> HALT bus speeds, I can correctly transfer commands and data to the HP
> 1350 (a listen only device). When the bus analyzer is removed, or
> connected and set to FAST the bus transfers
> will lock up at the inter-command "::" seperator characters. Its almost
> as if the HP 1350 cannot signal the bus that it needs to
> wait and think about the last command.
>
> What would happen if a HPIB listener could not drive NRFD?

I think that what may be wrong is a simple pull-up or pull-down resistor
(which may explain why the setup works with the bus analyser connected).

NRFD and NDAC are supposed to be "weakly" pulled high (so that even one
device pulling it low wins), so your 1350 may be allowing this line to
float rather than pulling it high. If the bus analyser is connected, it
will pull the line high (since the 1350 is floating the line) and the
bus cycle will work. With the bus analyzer removed, the line stays floating
and the cycle freezes.
Received on Sat Jun 21 2003 - 18:06:00 BST