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16 RELAY I/O CARD
2.1 Technical Description
The 16 Relay I/O Card relay output board provides two parallel input/output
(I/O) ports. The ports are organized as Ports A and B and are reed-relay output
ports. (See Table 2-1.)
Base Address
Port A Address:
Port B Address:
Note that Ports A and B are output ports with read-back capability. That means
that they can be written to (outputs) and then read back as inputs. Whatever was
written will always be read back (binary complement). This allows for bits to be set
or reset without altering the state of the other port bits.
2.2 Relay Output Circuit Description
The output ports on the 16 Relay I/O Card relay output are connected to 16 DIP
reed relays. Reed relays provide very-high-quality, long-life, low-current (10-watt
maximum), dry-contact switch closures. Reed relays are not suited for high-current
applications and can be destroyed by inductive load switching (where a spark
occurs across the contacts internally). The relays are normally open, and they close
when energized. Each relay can be individually energized by writing a "1" to the
proper port bit. Table 2-2 shows which bit controls which relay.
8
2. Introduction
Table 2-1. Port addresses.
Hex
Decimal
302
770
303
771
Mode
Output Port (Reed Relays)
Output Port (Reed Relays)
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