User manual

905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 10 © October 2001
Input signals connected to a module are transmitted to another module and appear as output signals.
These input signals may also be configured to appear as “inverted” signals on the output. A
transmission occurs whenever a "change-of-state" occurs on an input signal. A "change-of-state" of a
digital or digital internal input is a change from "off" to "on" or vice-versa. A "change-of-state" for an
analog input, internal analog input or pulse input rate is a change in value of the signal of 3%
(configurable from 0.8 to 75 %).
In addition to change-of-state messages, update messages are automatically transmitted on a regular
basis. The time period may be configured by the user for each input. This update ensures the integrity
of the system.
Pulse inputs are accumulated as a pulse count and the accumulated pulse count is transmitted regularly
according to the configured update time.
The I/O modules transmit the input/output data as a data frame using radio or serial RS485 as the
communications medium. The data frame includes the "address" of the transmitting module and the
receiving module, so that each transmitted message is acted on only by the correct receiving unit. Each
transmitted message also includes error checking to ensure that no corruption of the data frame has
occurred due to noise or interference. The module with the correct receiving "address" will
acknowledge the message with a return transmission. If the original module does not receive a correct
acknowledgement to a transmission, it will retry up to five times before setting the communications fail
status of that path. In critical paths, this status can be reflected on an output on the module for alert
purposes. The module will continue to try to establish communications and retry, if required, each time
an update or change-of-state occurs.
A system may be a complex network or a simple pair of modules. An easy-to-use configuration
procedure allows the user to specify any output destination for each input.
The maximum number of modules in one system is 95 modules communicating by radio. Each of these
modules may have up to 31 other modules connected by RS485 twisted pair. Modules may
communicate by radio only, by RS485 only or by both RS485 and radio. Any input signal at any
module may be configured to appear at any output on any module in the entire system. Systems with a
905U-C module and host device can have more than 95 radio modules.
Modules can be used as repeaters to re-transmit messages on to the destination module. Repeaters can
repeat messages on the radio channel, or from the radio channel to the serial channel (and serial to
radio). Up to five repeater addresses may be configured for each input-to-output link.
The units may be configured by using a PC connected to the RS232 port. The default configuration
and software configuration is defined in Section 4 Configuration.