Rockwell Automation 20-COMM-M Modbus/TCP Adapter - Manual (Page 92)

G-6 Glossary
20-COMM-M Modbus/TCP Adapter User Manual
Publication 20COMM-UM014C-EN-P
R Reference/Feedback
The Reference is used to send a setpoint (for example, speed, frequency,
torque) to the drive. It consists of one word of output to the adapter from the
network. The size of the word (either a 16-bit word or 32-bit word) is
determined by the drive.
Feedback is used to monitor the speed of the drive. It consists of one word
of input from the adapter to the network. The size of the word (either a
16-bit word or 32-bit word) is determined by the drive.
S Status Indicators
Status indicators are LEDs that are used to report the status of the adapter,
network, and drive. They are on the adapter and can be viewed on the front
cover of the drive when the drive is powered.
Subnet Mask
An extension to the IP addressing scheme that lets you use a single network
ID for multiple physical networks. A bit mask identifies the part of the
address that specifies the network and the part of the address that specifies
the unique node on the network. A “1” in the subnet mask indicates the bit
is used to specify the network. A “0” in the subnet mask indicates that the
bit is used to specify the node.
For example, a subnet mask on a network may appear as follows: 11111111
11111111 11111111 11000000 (255.255.255.192). This mask indicates that
26 bits are used to identify the network and 6 bits are used to identify
devices on each network. Instead of a single physical Class C network with
254 devices, this subnet mask divides it into four networks with up to 62
devices each.
Switches
Network devices that provide virtual connections that help to control
collisions and reduce traffic on the network. They are able to reduce
network congestion by transmitting packets to an individual port only if
they are destined for the connected device. In a control application, in which
real time data access is critical, network switches may be required in place
of hubs.
T TCP (Transmission Control Protocol)
Modbus/TCP uses this protocol to transfer packets using IP. TCP guarantees
delivery of data through the use of retries.
Z Zero Data
When communications are disrupted (for example, a cable is disconnected),
the adapter and drive can respond with zero data. Zero data results in the
drive receiving zero as values for Logic Command, Reference, and Datalink
data. If the drive was running and using the Reference from the adapter, it
will stay running but at zero Reference.