In the 15 years since its inception, the CAN bus has become the network of choice in automobiles and more recently has branched out to find a place on the factory floor. Now Microchip Technology Inc. is rolling out a microcontroller line that has something for both market sectors.
Based on the company's workhorse 8-bit microcontroller technology, the four devices in the PIC18Fx line come with flash memory for program storage, a small amount of EEPROM for calibration data or data logging, and expanded CAN bus capabilities. Depending on the amount of memory and I/O configuration, prices range from $7 to $8 in 10,000-unit quantities.
The CAN controller has three op-erating modes: as a drop-in replacement for older one-time-programmable (OTP) parts, another with some added buffers and filters, and a third that acts as a first-in, first-out (FIFO) message delivery system.
In legacy mode, designers can reuse application code that has already been developed for Microchip's OTP devices based on EEPROM technology. The big difference is in the program memory. Instead of EEPROM, the new devices use reprogrammable flash. Microchip, Chandler, Ariz., is also migrating from 0.7- to 0.5-micron design rules, allowing it to pack in twice as many memory bits as before, said product marketing manager Greg Robinson.
To expand the capabilities of the CAN interface, Microchip has added a second mode that includes six configurable transmit and receive buffers and 16 acceptance filters. A third mode sends messages directly to a FIFO stack, allowing users to find a message without an exhaustive search and pass it on to a data logger or an Ethernet bridge.
Microchip's move to expand the CAN capabilities of its MCUs comes when new offshoots of the bus protocol are springing up. Robinson said five variants have taken root in automobiles, a handful in the industrial sector, and still others for specialized engine control, such as boats and motorcycles.
One of these is DeviceNet, a network for industrial operation which, instead of the usual 11-bit structure, has a message identifier of 29 bits. DeviceNet has been codified in the CAN 2.0B specification, which the new Microchip parts support.
"CAN has become quite popular outside of automotive, and DeviceNet has helped push that in industrial control," Robinson said.