1. 主站（Master）：

   • 主站是网络的中央控制器，负责在预定的周期内与从站循环地交换信息。
   • 主站可以发送参数给从站，读取从站的诊断信息，用全局控制命令将它的运行状态告知给各从站。
   • 主站掌握总线中数据流的控制权，只要它拥有访问总线权（令牌），就可以在没有外部请求的情况下发送信息。
   • 在PROFIBUS-DP网络中，可以有1类DP主站（DPM1）和2类DP主站（DPM2）。DPM1是主要的中央控制器，而DPM2除了具有DPM1的功能外，还可以进行编程、诊断和管理等操作。

2. 从站（Slave）：

   • 从站是简单的输入、输出设备，例如传感器、执行器和变频器。
   • 从站只与它的主站交换用户数据，并向主站报告本地诊断中断和过程中断。
   • 从站不会拥有总线访问的授权，只能确认收到的信息或者在主站的请求下发送信息。

对于SST-PB3-PCU，要确定它是否是一个DP主站或从站，需要查看其具体的功能描述、技术规格以及它在PROFIBUS-DP网络中的角色。如果SST-PB3-PCU具有中央控制、参数发送、从站诊断信息读取等功能，那么它可能是一个DP主站。如果它只是作为输入/输出设备，与主站交换数据，则它可能是一个从站。

SST-PB3-PCU

In the PROFIBUS-DP network, there are concepts of master and slave stations.

Master:
The master station is the central controller of the network, responsible for cyclically exchanging information with the slave stations within a predetermined period.
The master station can send parameters to the slave station, read the diagnostic information of the slave station, and use global control commands to inform each slave station of its operating status.
The master station has control over the data flow in the bus, and as long as it has access to the bus (token), it can send information without external requests.
In the PROFIBUS-DP network, there can be Class 1 DP master station (DPM1) and Class 2 DP master station (DPM2). DPM1 is the main central controller, while DPM2 not only has the functions of DPM1, but can also perform programming, diagnosis, and management operations.
Slave:
Slave stations are simple input and output devices, such as sensors, actuators, and frequency converters.
The slave station only exchanges user data with its master station and reports local diagnostic interrupts and process interrupts to the master station.
The slave station does not have authorization for bus access, and can only confirm received information or send information at the request of the master station.
For SST-PB3-PCU, to determine whether it is a DP master or slave, it is necessary to review its specific functional description, technical specifications, and its role in the PROFIBUS-DP network. If SST-PB3-PCU has functions such as central control, parameter sending, and slave station diagnostic information reading, then it may be a DP master station. If it is only used as an input/output device to exchange data with the master station, then it may be a slave station.