RM signetics CAN mcu — Page
Microcontroller does control-area-network protocol in hardware
Protocol offers safety and real-time response for distributed control
systems
The 87C592 is an 8051 derivative microcontroller with on-chip hardware to
implement Control Area Network (CAN) protocols. CAN is a serial
error-correcting bus developed by Robert Bosch A.G. for automotive use
that may become a standard for multiplexed wiring in other applications as
well. The CAN protocol is a one-or-two-wire protocol aimed at safety and
reliability in a noisy environment. It has unlimited nodes, star or bus
topology, and allows all nodes to master. Each data frame can carry up to
8 bytes of useful data. It also carries a 15-bit CRC sequence and various
control bits. It specifies transfer rates of 1 Mbit/s up to 40 m, tapering
to about 10 Kbits/s at 10 km. The actual top data rate is 577 Kbit/s, the
remainder being the frame and interframe space. Error detection
capabilities include up to five randomly distributed errors by CRC, any
odd number of errors by parity, and burst errors up to 14 bits. Any time 5
bits of the same sign occur in the data, the sender inserts an opposite
bit. Thus any time 6 or more bits of the same sign come in, an error is
detected. The probability of an undetected error is 10
message. The message ID, either 11 or 29 bits, includes priority
information that controls bus arbitration. Each node reads as it sends,
and the lower-priority sender will be the first to detect a conflict in the
ID string and get off. High-priority messages have a guaranteed latency of
not more than 134 microsecond at the top data rate. Its combined
real-time nature and reliability make CAN usable in safety-related
applications, such as antiskid braking and collision avoidance. They also
suit it to medical instrumentation. CAN has been licensed by Intel,
Motorola, and National Semiconductor, in addition to Philips/Signetics.
ROM and ROMless versions of the '592 are coming next year. (P87C592EHA in
OTP plastic, $35 ea/100–available now.) Signetics Co., Sunnyvale, CA
Mike Thompson 408-991-5207
CAPTION:
The 87C592 microcontroller has on-chip hardware for the CAN protocol,
intended for multiplexed automotive electronics.
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