660-MISC-3311模塊卡件,ABB參數說明660-MISC-3311
Modbus主機將發(fā)出啟動事務的命令。該命令將包含一個單元
指定應響應的從機的地址。從機將處理該命令并返回單個響應。通過使用消息中包含的校驗和來確保消息的完整性。從機忽略所有具有無效校驗和的消息，并假設主機已接收到發(fā)送的任何響應。主節(jié)點應用程序負責提供超時和重試條款。在RTU模塊適當響應Modbus命令之前，必須將其配置為公共線路上其他裝置使用的幀協議。
660-MISC-3311模塊卡件這包括介質（RS）等項目-485、RS-232或調制解調器）、幀協議，如（ASCII、RTU、ASCII-A或RTU-A）、波特率、奇偶校驗、，停止位，最后是可選的握手。
3.2端口選擇用戶可以選擇RS-232、RS-485或調制解調器通過PLC進行通信軟件配置。RS-232和RS-485端口的引腳如下所示。的引腳調制解調器端口在第14頁。RTU模式以二進制形式發(fā)送每個字節(jié)的信息，因此需要8位傳輸數據。ASCII碼模式將信息字節(jié)分為兩個半字節(jié)，并將每個半字節(jié)作為7位十六進制字符傳輸。ASCII模式使用兩倍的傳輸字符；但是，使用可打印ASCII進行調試角色可以容易得多。因此，將模式設置為ASCII或RTU間接設置數據大
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
