Elpro Technologies 905U-D User Manual download pdf (Page 27)

Chapter Three Operation

Page 27 © January 2011

Up to five repeater addresses may be configured as part of the remote address. That is, up to 5

intermediate modules can act as repeaters between the master and slave modules.

The RS232 DTR signal can be configured to act as a disconnect signal. If so configured, the

DTR signal will force a hang-up (DCD reset) if the host device resets the DTR signal.

3.6.4 Fast Operation Controlled Mode

This configuration does not allow the use of repeater addresses. In fast operation mode, the

master unit continually communicates with the slave such that any data transfer can be achieved

with a small lead-in (approx 5 msec). The operation is similar to single-connect mode.

3.6.5 CTS/RTS Flow Control

Flow control is a configurable parameter. On the RS232 port, if CTS/RTS is enabled, the CTS

signal will be active when the input data buffer is not full. Note that CTS/RTS is disabled in the

default configuration - if this feature is required, it must be enabled (refer Configuration

Chapter 4). If CTS/RTS is not enabled, then data will be lost after the input buffer (2KB) is

full.

3.6.6 Intermediate Repeaters

Where intermediate repeaters are configured, each repeater will re-transmit the message onto the

next address. When the destination address is reached, the destination module will return an

acknowledgment (ACK) with the reverse address structure as the received message.

If error-checking is selected, then the destination module will only return a ACK if the error

check is valid. If the error check is not valid, then no ACK message is returned. If the error-

checking function is not selected, then the destination module will return an ACK every time it

receives a message. Each repeater will re-transmit the ACK message until it is received by the

source module.

The source module will calculate a waiting time for the acknowledgment - this time is based on

the radio baud rate, the message length (number of bytes) and the number of repeaters. If the

source module does not receive an ACK, it will transmit the same message again. The 905U-D

will transmit the message up to five times. If it does not receive an ACK after the 5

attempt, it

will assume communications failure and reset its DCD status. The unsuccessful message will

not be re-transmitted and will be lost.

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Elpro Technologies 905U-D User Manual Page 27