ADInstruments PowerLab/16SP, Owner'S Manual

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36 PowerLab Owner’s Guide
to 25-pin cable. If you are using a Windows PC, the connection at the
other end of the cable depends on your set-up.
SCSI is sensitive to cable impedances and connection lengths. The
incorrect wiring of a SCSI cable can result in damage to the SCSI
circuitry, or random SCSI activities being performed. You should,
therefore, use only approved SCSI cables such as the ones available
from ADInstruments, and never attempt to make your own.
I
2
C Expansion Port
The I
2
C port on the back panel of the PowerLab provides expansion
support for ADInstruments front-ends. This port provides both
power and control signals for these front-ends. The I
2
C bus has a
daisy-chain structure that allows simple connection of additional
front-ends to the system. A PowerLab can have as many front-ends
connected to it as it has analog inputs, roughly speaking. You should
not attempt to run other external devices from the I
2
C port: it is
designed for use only with ADInstruments front-ends. Only 50 mA
maximum current can be provided through this bus, so it should not
be used for third-party devices drawing more current.
1 5
9 6
DGND UNREG–20 V UNREG+10 V UNREG+20 V
Front-end power
SCL DSC SDA DSD INT
I
2
C control signals
Figure A–9
The 25-pin SCSI connector
Figure A–10
The pin assignments for the
I
2
C port