DSSA165 Secure Digital Applications

DSSA165 Secure Digital Applications

Control Builder supports a number of serial communication protocols for Compact Control Builder products and third party HMI. These protocols can be used for communication between PLCs, as well as with other devices.

Function blocks in SerialCommLib allow implementation of a personal character oriented protocol on a serial port. It supports writing an application that both controls the characters sent and checks that the correct answer is received by using various checksum algorithms.

The serial protocol can only be executed in half duplex. Accordingly it can not send and receive simultaneously. The following function block types are available:

• SerialConnect

• SerialSetup

• SerialWriteWait

• SerialListenReply

• SerialWrite

• SerialListen A maximum 140 characters is supported.

ASCII telegrams are recommended, since binary telegrams are difficult to implement.

In cases where all PLCs must use the same time, for example when time stamps are useful, clock synchronization is needed. AC 800M supports clock synchronization by five different protocols – CNCP, SNTP, SNTP on CI, MB 300 Clock Sync and MMS Time Service.

CNCP is the normal protocol for clock synchronization on the Control Network. An AC 800M PLC selected as Clock Master multicasts synchronization messages on the network.

PLCs with PM861, PM864, PM866 and PM891 processors can be configured for CPU redundancy. Two CPU modules are then run in parallel, one as primary and one as secondary. If the primary CPU fails, the secondary CPU automatically takes over.

The AC 800M PLCs contain a card slot located at the front of the PLC. This card slot supports backup media cards. It is possible to restore the saved configuration data and firmware data from the backup media card to the PLC. The supported backup media cards for AC 800M PLCs are:

• Compact Flash (CF) card (supported in all AC 800M PLCs except PM891).

• Secure Digital (SD) card (supported only in PM891).

The CF/SD memory card helps to store a compiled PLC configuration to the card and then install it into the PLC by inserting the CF/SD card. This makes it easy to distribute new software upgrades to PLCs in different locations which are not networked. The control software is installed without requiring any tool.

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