Reflective Memory is a fiber-optic high-speed deterministic network that allows multiple devices to share large amounts of data quickly and efficiently. Data is transferred by writing to on-board global RAM. The data is automatically sent to the same location in memory on all Reflective Memory boards on the network.

The new Reflective Memory interface allows data to be shared between up to 256 independent systems (nodes) at rates up to 6.2 Mbytes per second. Each Reflective Memory board is configured with 256 Kbytes of on-board SRAM. The local SRAM provides fast read access times to stored data. Writes are stored in local SRAM and broadcast to other Reflective Memory nodes. The transfer of data between nodes is software transparent, so no I/O overhead is required.

 Application Benefits

•  High-speed, performance-based 170 Mbaud network for high-speed applications such as rolling mills and assembly lines.

•  User’s ladder-logic program can read and write directly in reflective memory for sharing with other PLCs or computers.

•  Each PLC or computer keeps a local copy of shared data for fast real-time use.

•  No special protocol or software needed. It is treated just like memory.

•  High-reliability, fiber-optic (noise immune) connection between PLCs and computers.

•  No high-performance LAN is as easier to install and operate. No software is needed to operate the board in its power-up state.

• Reading data memory (any reflective memory board on the network) will appear at the same address at all other node’s reflective memory boards. This is the same address that data was originally written into from the sending reflective memory board.

• Reflective Memory bus platform support includes VME, PCI, PMC and Multibus platforms. The multiple platform support enables a wide range of applications to be fulfilled.

Product Features

• Interrupts

The Reflective Memory allows interrupts to one or more nodes by writing to a byte register. These interrupt signals (three levels, user definable) may be used to synchronize a system process or used to indicate new data has arrived.

• Link Arbitration

The network is a fiber-optic daisy chain ring. Each transfer is passed from node to node until it has gone all the way around the ring and reaches the originating node. Each node retransmits all transfers that it receives except those that it originated. Nodes are allowed to insert transfers between transfers passing through.

• Error Management

Errors are detected by the Reflective Memory module with the use of the error detection facilities of the TAXI chipset and additional parity encoding and checking. The module can be operated in a redundant transfer mode in which each transfer is transmitted twice. In this mode of operation, the first of the two transfers is used unless an error is detected, in which case the second transfer is used.

• Network Monitor

There is a bit in a Status Register that can be used to verify that data is traversing the ring (that is, the ring is not broken). This can also be used to measure network latency.

For an overview on Reflective Memory, visit VMIC and download the Reflective Memory data sheet.