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GPIB / HP 53131A
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This is a set of captures of traffic with an HP53131A counter using an
AR488 (Arduino bitbang GPIB adapter).


Logic analyzer setup
--------------------

The logic analyzer used was a generic FX2 board (at 500kHz):

  Probe       GPIB
  ----------------
  0           DIO1
  1           DIO2
  2           DIO3
  3           DIO4
  4           DIO5
  5           DIO6
  6           DIO7
  7           DIO8
  8           EOI
  9           DAV
  10          NRFD
  11          NDAC
  12          IFC
  13          SRQ
  14          ATN
  15          REN


hp53131a-idn-read.sr
--------------------

Send *idn? and receive instrument ident string.
Send 'read?', wait for acquisition and receive a measurement (10MHz frequency).


hp53131a-ton.sr
---------------

Set HP53131A to period measurement and talk-only mode and AR488 to
listen-only mode.

This setup is specifically useful for recording long logfiles of timing data
for use in ADEV measurements by "time-nuts":

  http://www.ke5fx.com/timelab/readme.htm 

Note: the regular NRFD/NDAC handshake occurring before and after the LON
transfer is related to the AR488 timing out non-existent transfers and may
be incorrect.