西门子S7系列串口通讯模块的信息与使用8.常见问题:CP341模板和调制解调器之间的通讯
日期：2008-3-20 19:04:00 来源： 作者：51plcjs 点击：
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ANSWER:
The modules CP341 and CP441 have different default settings for the V24 output signals DTR and RTS after return of power: the CP441 starts up with DTR = RTS = 1 and the CP341 with DTR = TRS = 0.
As a result of DTR = 0 the SATEL modem puts the Receive line of the CP341 (RxD) into BREAK and in this state sending is not possible.
With reference to the interfacing of modems, when assigning the parameters for the CP341 in the hardware configuration, you have the option 'Automatic operation of V24 signals'. With this setting the CP341 sets its DTR statically to 1 and also the RTS before each 'Send'.
However, this setting requires correct response behavior of the modem that is not provided by the SATEL modem. Other modems acknowledge the set DTR of the CP with set DSR or the set RTS of the CP with set CTS. If the DSR and CTS remain at 0 (as with SATEL), then a corresponding error message is generated and the Send procedure aborted.
Remedy:
In order to realize communication between the CP341 and the SATEL modem after resumption of power you have to call block FC6 (V24_SET), for example, in OB1. The parameters RTS and DTR must then be set to 'TRUE'.
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