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Schematically, what does a MACRO network look like?
MACRO operates in a ring topology (see above sketch). Data is transmitted serially. Each station on the ring has an "in" port for receiving data and an "out" port for transmitting data. Nodes, residing at a station, can be amplifier axes, I/O banks, or communication interfaces to other devices. A station can have one or several nodes, allowing for multi-axis amplifiers with a single "in" and single "out" port. Data packets, (groups of 96 bits of serial data), sent out by a motion controller or, master node, are earmarked for a specific amplifier, or slave node. If the data packet is not for an amplifier, it passes it on, unchanged. If it is for the node, it copies the contents of the data packet (typically commands), places feedback data into the packet in place of the command data, and transmits the data packet.
What happens at a node?
The operation of MACRO is based on standard FDDI (Fiber Direct Digital Interface) networking technology. In the illustration below, data written to MACRO from a processor, is shifted out via byte wide shift registers. These shift registers (typically embedded in an
ASIC) send bytes of data to a Network Interface Driver IC which serializes the bytes of data, and outputs a serial stream at 125
Mbits/sec. The network driver adds 2 bits of error detection to the byte and puts out the data in a 4B/5B coding scheme. This serialized digital data is then routed through an optical or electrical driver for transmission to remote nodes.
At the receiving node, essentially the reverse process happens. An optical or electrical receiver receives the data stream and funnels it into a network interface receiver IC. Here, the data is de-serialized and clocked into shift registers in 4B/5B protocol.
An address specifier at the beginning of data packets indicates whether or not the data following in the packet is intended for the node. If it is not, it is put right back onto the ring via the process just described and graphically illustrated as Case 1 below. If however, the data is for the node, a simultaneous "copy and replace" process is performed as shown in Case 2.
Transparent ring interface.
Since the MACRO shift registers manage the communications (shifting data out and in to the ring at the appropriate times), the network transmission is transparent to the controller software. If information is required, a register is simply read. If there is a need to transmit information, it is merely written to a register... MACRO hardware does the rest! This parallel register interaction makes MACRO quick, simple and efficient for a processor to interact with the MACRO ring.
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