Allen-Bradley Driver Tag Type Properties: Serial Tab
The Serial tab for the Allen-Bradley driver tag properties folder consists of attributes used to identify and establish a connection the serial port tag that the Allen-Bradley driver should use to transmit data to the I/O device. The Serial tab is also used to select the communication protocol and error checking to be used in transmissions of data between the I/O device and the Allen-Bradley driver.
(Click title to expand text)
The Port field enables you to select the serial port tag or TCP/IP tag you wish to be associated with this driver tag. A serial port tag opens a serial port to enable communications between VTS and your PLC or RTU. A TCP/IP tag enables you to connect to a series of hosts, allowing you to transmit data across a network or over the Internet.
The Port field can be used to associate this tag with a new or existing serial port tag or TCP/IP tag using the … button. The … button opens the Tag Browser, which displays only the existing serial port and TCP/IP tags for your application, and enables you to create a new serial port or TCP/IP tag using its New button.
The Port field can be cleared using the X button that appears to its right.
Right-clicking the name of the serial port or TCP/IP tag that has been selected in the Port field opens the tag properties folder for the selected tag.
The Time-Out Limit field indicates the receiver time-out limit (i.e. the time in seconds or fractions of a second that this driver should wait for a reply from the PLC or RTU).
The VTS Station Address (Octal) field enables you to specify the address (using the octal addressing format) of the VTS system on the serial link.
The Retries spin box enables you to select the number of attempts that will be made by this driver if there is no reply to a message, before an error is declared.
The ENQ Delay field enables you to specify the amount of time (in seconds or in fractions of a second) that this Allen-Bradley driver should wait before sending an ENQ in half duplex mode.
Note: Half duplex mode refers to the transmission of data in one direction at a time.
The RTS Key Off Delay field represents the amount of time (in seconds) that this Allen Bradley driver will wait before dropping RTS at the end of a data transmission.
The Hold checkbox indicates whether this driver should hold data from the PLC or RTU in the event of a communications failure.
If the Hold checkbox is selected, the last received value from the PLC or RTU will be held.
If the Hold checkbox is not selected, the data will be invalidated in the event of a communications error.
By default, the Hold checkbox is not selected.
Click this checkbox to select whether the BCC error checking method will be used on communication messages.
By default, the BCC checkbox is not selected (i.e. CRC error checking is used on all communication messages).
Note: The CRC acronym stands for Cyclic Redundancy Check, and the BCC acronym stands for Block Check Character. Both are techniques used to detect data transmission errors. In general, CRC is a better error checking method, as it is a 16-bit error check, whereas BCC is an 8-bit error check
Enables you to choose between the following data transmission modes in communications from the driver to the PLC.
• Half Duplex: Half duplex mode refers to the transmission of data in one direction at a time. If the driver and the PLC are communicating using the half duplex mode, either the driver or the PLC may transmit data at one time. The device not communicating must wait until the device that is transmitting data is finished before it can transmit its data.
• Full Duplex: Full duplex mode refers to the transmission of data by both parties simultaneously.
• Radio Modem: Certain Allen Bradley PLCs implement the Radio Modem Protocol (RMP) to optimize DF1 communication on radio modem links. The protocol is an enhancement of the Full Duplex Protocol and uses the same message format with all the ACK and NAK responses removed.