Reflective Memory Card: Installation

Some of the required settings controlled by the switch settings are as follows.

• Node ID
• Redundant Transfer Mode
• Rogue Packet Detection and Removal

A more complete explanation of the switches and their impact on operation of the network can be found in the hardware reference manual for your card.

Node Id

Each card on the network must have a unique Node Id to identify itself. Nodes are numbered from 0 to 255. The factory settings for the reflective card set the Node Id to be 0 (zero). There are no reserved network node Id???s, but there is no inherent detection of duplicate nodes on a network.

Redundant Transfer Mode

When redundant transfers are enabled, each packet is transferred twice. If the first packet is received without error by the receiving circuitry, then the second transfer is discarded. If an error occurs on the first transfer and the second transfer has no transmission errors, then the second transfer is used to update the onboard memory. If both transfers are unsuccessful, the data is not re-transmitted on the network. Using a redundant transfer mode reduces the likelihood that packets will be dropped from the network, but at a significant cost of a lower network data transfer rate.

Rogue Packet Detection and Removal

A rogue packet is a packet that does not seem to belong to any node on the network. If the packet is altered as it passes through a non-originating node or if the originating node begins to malfunction, the originating node may fail to recognize the packet as its own and will not remove the packet from the network. In such circumstances the packet passes around the network loop indefinitely.

Rogue packets are rare. Their existence indicates a malfunctioning board due to component failure or operation in an overly harsh environment. Normally, the solution is to isolate and replace the malfunctioning card or improve the environment. However, in some applications it is preferable to tolerate sporadic rogue packets rather than halt the system for maintenance, provided the rogue packets are removed from the network.

To prevent rogue packets from circulating on the network indefinitely, reflective memory cards can be configured to operate as one of two rogue masters.

A rogue master alters each packet as it passes through its node. If that packet returns to the rogue master a second time, the rogue master recognizes that it is a rogue packet and removes it from the network.

The reflective memory network supports up to two rogue masters per network, Rogue Master 0 and Rogue Master 1, so they can cross check each other.

1. Node Id.
2. Redundancy Mode.
3. Rogue Master Setting.