module. The inputs are isolated from the logic by bi-directional
optocouplers. The common is connected internally to either the - volts
or +volts field power supply terminals using a jumper link which is
situated inside the housing. The inputs have internal counters
associated with them. These counters are 32 bit counters allowing a
count value from 0 to 4294967295. The count value can be cleared by
writing a zero to the associated registers or preset to any other value
using the same method. The counters can also be reset automatically
when read. This is done by setting on DIP switch 9 on the front panel.

Note: The count values are not battery backed-up and will be lost if
power is turned off.

The format of the registers allows the status of the inputs to be read as
either single bits or all at once as a single register on the Modbus
network. The 8 digital outputs are open collector (NPN). The outputs
may be used to drive lamps or external relays when more drive
capability is required. The outputs are isolated from the logic and they
share a common negative terminal.

The module may be used as either a slave or master on the Modbus
network. When used with a PC or PLC the module will be configured
as a slave. When used with another PL8DIO module in a point-to-point
configuration, the DIP switch 9 must be turned on to set the module up
as a master. In this mode the PL8DIO module will automatically
read/write the information from/to the other PL8DIO module.

When used as a slave module, the outputs are written to by the
Modbus master device such as a PC or PLC. Each output can be
individually switched on or off, or all outputs can be set up at the same
time by writing a single number to the output register which represents
the status of all outputs.
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