SCRAMNET OVERVIEW
Copyright 2007
2-4
S SC150e HARDWARE REFERENCE
2.3.4 Receiver FIFO
The Receiver FIFO is designed as a temporary holding place for incoming foreign
messages while the shared memory is busy servicing a host request. This FIFO is three
messages deep, and is designed so it can never be overrun. Each item in the Receiver
FIFO contains 21 bits of address (A22 - A2), 32 bits of data, and one incoming interrupt
bit. When the messages are 1024 bytes, the initial header information data stays in the
FIFO, the subsequent four bytes of data are loaded in, and the address is incremented by
four.
2.4 Network Ring
The S SC150e Network is a ring topology network. Data is transmitted at a
rate of 150 Mbits/s over dual fiber-optic cables. Together, the two lines produce the
incoming data clock. Due to the network speed and message packet size, the network can
accommodate over 1,800,000 message packets passing by each node every second. There
is an approximate 247 ns (minimum) delay at each node as the message packet works its
way around the ring. The maximum delay depends on the selection of fixed-length or
variable-length message packets. A fixed-length message packet has a maximum delay of
800 ns, a 256-byte variable-length message packet is 16.2 µs, and a 1024-byte variable-
length message packet is 62 µs. Delay can be imposed when a node must complete the
transmission of a native message packet before retransmitting a foreign message packet.
A S SC150e
Network can accommodate up to 256 nodes per network ring.
2.4.1 Protocol
The protocol is a register-insertion methodology and is NOT a token ring. Depending on
the protocol selected, all message packets are the same size or are variable (as in the
PLUS modes), and multiple nodes can transmit data simultaneously. There is no master
node, and all nodes have equal priority for network bandwidth. The message protocol is
designed specifically for real-time applications where data must be passed very rapidly.
When the node operates in BURST or BURST PLUS mode, the node will never re-
transmit its own messages for error correction. When operating in PLATINUM or
PLATINUM PLUS mode, error detection is enabled, and re-transmission can occur.
BURST MODE
BURST
mode is an open loop, non-error-corrected communication mode. This mode
allows multiple 82-bit messages (46-bit header plus 32-bite data and four parity bits) per
node on the ring at a time. The limited-message-packet length enhances the data latency
characteristics of the network by providing the shortest possible media access delay. The
messages are transmitted as fast as the system will allow.
PLATINUM MODE
PLATINUM mode is BURST mode with error correction enabled. The messages are
transmitted as fast as the system will allow, but error checking is used to detect and re-
transmit corrupted message packets.
Содержание SCRAMNet+ SC150e
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