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发表于 2018-1-2 22:47:17
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本帖最后由 zchong 于 2018-1-2 22:50 编辑
找到一个网页http://www.simplymodbus.ca/TCP.htm
截取部分内容如下:
Modbus RTU over TCP
Simply put, this is a Modbus RTU message transmitted with a TCP/IP wrapper and sent over a network instead of serial lines. The Server does not have a SlaveID since it uses an IP Address instead.
Modbus TCP
A Modbus Messaging Implementation Guide provided by Schneider Automation outlines a modified protocol specifically for use over TCP/IP. The official Modbus specification can be found at www.modbus.org/specs.php . The main differences between Modbus RTU and Modbus TCP are outlined here.
看上去Modbus RTU over TCP意思就是把rtu的数据帧直接打包成TCP包发送,而Modbus TCP则是修改了协议帧本身,提出了一个MBAP Header。
实际使用时Modbus RTU over TCP和Modbus TCP那个应用的多些呢? |
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