GE DS200SDCIG1AEB模拟量驱动控制卡
PQM始终是Modbus从站；它不能被编程为Modbus主机。计算机或PLC通常被编程为主机。Modbus协议有两种版本：远程终端单元（RTU，二进制）和ASCII。PQM仅支持RTU版本。使用读写寄存器命令可以实现监控、编程和控制功能。7.1.2电气接口电气接口为2线RS485和9针RS232。在2线RS485链路中，数据流是双向和半双工的。也就是说，数据从不同时发送和接收。RS485线路应以菊花链配置（避免星形连接）与安装在链路两端的终端网络连接，即主端和离主端最远的从端。当与Belden 9841 RS485电线一起使用时，终端网络应由一个120Ω电阻器与一个1nF陶瓷电容器串联组成。
The PQM is always a Modbus slave; it cannot be programmed as a Modbus master. Computers or PLCs are commonly programmed as masters. The Modbus protocol exists in two versions: Remote Terminal Unit (RTU, binary) and ASCII. Only the RTU version is supported by the PQM. Monitoring, programming and control functions are possible using read and write register commands. 7.1.2 Electrical Interface The electrical interface is 2-wire RS485 and 9-pin RS232. In a 2-wire RS485 link, data flow is bi-directional and half duplex. That is, data is never transmitted and received at the same time. RS485 lines should be connected in a daisy-chain configuration (avoid star connections) with a terminating network installed at each end of the link, i.e. at the master end and the slave farthest from the master. The terminating network should consist of a 120 Ω resistor in series with a 1 nF ceramic capacitor when used with Belden 9841 RS485 wire.
