660-MISC-3311模块卡件,ABB参数说明660-MISC-3311
Modbus主机将发出启动事务的命令。该命令将包含一个单元
指定应响应的从机的地址。从机将处理该命令并返回单个响应。通过使用消息中包含的校验和来确保消息的完整性。从机忽略所有具有无效校验和的消息，并假设主机已接收到发送的任何响应。主节点应用程序负责提供超时和重试条款。在RTU模块适当响应Modbus命令之前，必须将其配置为公共线路上其他装置使用的帧协议。
660-MISC-3311模块卡件这包括介质（RS）等项目-485、RS-232或调制解调器）、帧协议，如（ASCII、RTU、ASCII-A或RTU-A）、波特率、奇偶校验、，停止位，最后是可选的握手。
3.2端口选择用户可以选择RS-232、RS-485或调制解调器通过PLC进行通信软件配置。RS-232和RS-485端口的引脚如下所示。的引脚调制解调器端口在第14页。RTU模式以二进制形式发送每个字节的信息，因此需要8位传输数据。ASCII码模式将信息字节分为两个半字节，并将每个半字节作为7位十六进制字符传输。ASCII模式使用两倍的传输字符；但是，使用可打印ASCII进行调试角色可以容易得多。因此，将模式设置为ASCII或RTU间接设置数据大
The Modbus master will issue a command to start the transaction. The command will contain a unit
address specifying the slave which should respond. The slave will process the command and will return
a single response. Message integrity is assured through use of checksums included in the messages.
The Slave ignores all messages which have invalid checksums and assumes the Master has received
any responses sent. It is the Master node application’s responsibility to provide time-out and retry
provisions.
Before the RTU Modules will respond appropriately to Modbus commands it must be configured to the
frame protocol used by the other unit on the common line. This includes items such as the media (RS-
485, RS-232, or modem), frame protocol such as (ASCII, RTU, ASCII-A, or RTU-A), baud rate, parity,
stop bits, and, finally, optional handshaking.
3.2 Port Selection
The user may select either the RS-232, RS-485, or modem to use for communications through the PLC
software configuration. The pinouts for the RS-232 and RS-485 ports are shown below. The pinout for
the modem port is on page 14.RTU mode sends each byte of information in binary form thus requiring 8-bits of transmitted data. ASCII
mode divides a byte of information into two nibbles and transmits each as a 7-bit hexadecimal character.
The ASCII mode uses twice as many transmitted characters; however, debugging with printable ASCII
characters can be much easier. Therefore, setting the mode to either ASCII or RTU indirectly sets
whether the data size is 7 or 8 bits. The second (alternate) set, ASCII-A AND RTU-A, selects a new
