Handshaking in Serial 485 Two Wire Modes Hardware: Serial>>RS-485
Problem: I could not find any documentation on when the CTS, RTS, and DTR lines are used in the Serial 485 - Two Wire Transceiver Modes. What are these for? Solution: The use of the CTS and RTS lines are independent of the transceiver mode. The CTS and RTS lines are only used in handshaking when hardware handshaking is enabled. If software handshaking is used, the CTS and RTS lines do not need to be connected. DTR is an internal line for the transmitter and receiver that allows them to be turned on and off depending on the wire mode. In Two Wire DTR Control with Echo and Two Wire DTR Control without Echo, the DTR line is used to enable the transmitters. This DTR line does not directly affect the CTS or RTS lines. You can assert or deassert the DTR line by using the NI-VISA Modem Line Settings: Line DTR State property nodes in LabVIEW or the VI_ATTR_ASRL_DTR_STATE in C. Related Links: KnowledgeBase 17M6L0TI: What Are the Different Transceiver Modes on the NI RS-485 Serial Cards? KnowledgeBase 1M9E1L6Q: Serial Communication General Concepts KnowledgeBase 3BJC7JXR: How Do I Set and Get the Serial RS-485 and RS-232 Transceiver Wire Modes Programmatically in LabWindows/CVI? Attachments:
Report Date: 10/28/2004 Last Updated: 10/07/2005 Document ID: 3ERB66VB |
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