The land-line modems are considered to be DCE or Data Communications Equipment. Computers, PLCs and RTUs are usually considered to be DTE or Data Terminal Equipment. The DTE or Data Terminal Equipment often needs the modem to be set at a fixed rate so the serial baud rate stays the same from the calling computer through the modems to the answering modem. This rate is usually automatically detected on initialization. After a power cycle, though, this setting can be lost. To set the fixed serial rate despite a power cycle the AT+IPR command can be used before the first call after the AT&F command is sent.
Use Case: Configuring the VT-MODEM to have a fixed DTE Rate
VT-MODEM Set-up Wizard
Match the VT-MODEM Set-up Wizard configuration with DTE speed
- The first setting to consider in the VT-MODEM Setup Wizard is the Computer/Modem port settings. The settings here should match the PLC/RTU/Controller that the answering modem. This setting will set the serial modem to match these settings.
- Baud rate may be lost after a power. To set the modem speed to be remembered even if the power is cycled use the IPR setting (Fixed DTE Rate). Enter +IPR=<rate>. In this case since the baud rate was previously set at 9600 the rate in the screen grab below is 9600, but this setting can be set to 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200.
Set the +IPR setting using the VT-MODEM setup wizard.
- Setting the +IPR=<rate> command by itself after some connections have been made will result in faulty connections. Using the VT-MODEM set-up wizard will ensure that the modem is properly reset and configured.
- If the +IPR command is used with out the VT-MODEM set-up wizard you must precede the command with the AT&F command. This will reset the modem and may reset other settings required in the configuration.
It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.
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