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6
Using the Pin Matrix Cards
Protection Bypass
C A U T I O N
Reset State
User Connectors and Pinouts
6-8
Each of the four columns has a 200 ohm protection resistor
connected in series which protects the relays by limiting the
maximum current through the column. Some measurements
(such as 2-wire resistance) may require bypassing (shorting
across) the protection resistor to remove its effects. The default
state is to have the protection bypass relays open, which means
the series protection resistors are in circuit.
Bits 7-4 in the ABus Control & Protection Bypass Register
(described in Appendix B) control the relays used to bypass the
series protection resistors. You can bypass the protection on a
column-by-column basis.
To prevent damage to card, bypass the protection resistors
only when absolutely necessary.
Figure 6-4 Column Disconnect and Protection Bypass Relays
Column (n)
The card resets to its default state whenever:
• Operating power is first applied,
• Operating power is removed and then reapplied,
• Bit 0 in the Control register (described in Appendix B) is
asserted.
When the card is reset, all relay registers are cleared, column
disconnect relay control is set to automatic mode, and the relay
timer is started.
The figures and tables on the following pages show the pinouts
for the Agilent E8792A and E8793A user connectors.
Bypass
Relay
Disconnect
200
E6198B Switch/Load Unit User Manual
Abus (n)
Relay
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