210 SI-Ethernet User Guide
Issue: 3
Patch lead: A network cable where the terminal connections at one end of the cable are connected
straight through to the other end on a pin to pin basis. Normally used to connect a network device to
a network switch.
PC: Personal Computer.
PDU: Protocol Data Unit. This is the main Modbus message telegram, to which is added the MBAP
header to form the complete Modbus telegram.
PLC: Programmable Logic Controller.
Poll rate: The rate at which cyclic data is sent and received on the network.
Polled data: See Cyclic data.
Router: A device that is used to connect different networks or subnets, in a similar way to a firewall,
however a router generally allows significantly less control of the data.
RPI: Requested Packet Interval. Specifies the expected time for the device to respond to a request.
Scan rate: See Poll rate.
Shielding: A connection to provide additional immunity to noise used on a network cable.
SMTP: Simple Mail Transfer Protocol. A protocol used for sending email.
SNTP: Simple Network Time Protocol. A protocol used for synchronising time over a network.
Status word: A value that denotes the status of the drive. Each bit within the word will have a
specific meaning.
Subnet: A part of a network that has IP addresses in the same range. Devices on the same subnet
may communicate directly with other devices on the same subnet without the use of a gateway.
Subnet mask: Defines which part of the IP address constitutes the subnet address and which part
constitutes the host device address.
Switch: A device that allows Ethernet devices to be interconnected.
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