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Relay Timer
OAR
Reset
Protection Bypass
C A U T I O N
E6198B Switch/Load Unit User Manual
The Relay Timer indicates whether or not the last change to a
relay's state (opening or closing the relay) is complete. The
timer starts or restarts when a command to change a relay's
state is received. The timer stops when it times out after an
interval sufficiently long for a relay to change state. If the relay
timer's status is "busy," as reported by bit 7 of the Status
Register (see
Appendix
state. If the status is "not busy," then the relays have reached
their newly programmed state. The nominal time-out value of
the relay counter is 500 us.
Bit 5 in the Control Register controls the OAR ("open all relays")
feature, which immediately opens all relays on the card.
Because the bit is self-clearing, it does not require resetting.
OAR also clears bits 3-0 of the Column Control & Protection
Bypass Register. When executed, OAR re-triggers the relay
timer.
Bit 0 in the Control Register programmatically resets the card.
Resetting the card clears all internal registers, which resets all
board functionality to its default, power-up state. Resetting also
clears all relay registers and starts the relay timer.
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 3-0 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, bypas the protection resistors only
when absolutely necessary.
Using the Pin Matrix Cards
B), relays may not yet be in the desired
6
6-21
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