The shift to 32-bit microcontrollers has been dramatic, but there is still a solid market for 8-bit devices. Compact, inexpensive chips are being used to drive LEDs (light-emitting diodes) and motors remotely, using the LIN (Local Interconnect Network) protocol to provide low-cost links to centralized 32-bit electronic control units.
Though 32-bit devices are the hot growth area, inexpensive 8-bit devices still account for nearly half the microcontrollers in a typical vehicle. This year, Strategy Analytics predicts that cars will have an average of 10.7 low-end 8-bit controllers, rising to 12.7 units per vehicle in 2016. The 32-bit CPU (central processing unit) market is now at 4.9 units per vehicle, rising rapidly to 7.9 in 2016. Also, 16-bit usage will be fairly flat, rising from 6.4 to 6.6 units per vehicle in 2016.
Several factors drive demand for 8-bit chips. They are small enough to sit near motors and LED banks, they draw little power, and they do not cost much. They are also seeing use in emerging areas such as advanced instrument clusters.
Microchip Technology Inc. recently focused on power conservation with a line of 8-bit PIC microcontrollers that have active currents of less than 50 µA per MHz and sleep currents down to 20 nanoamps. They also offer up to 50% increase in performance, and 14 added instructions that yield up to 40% better code execution over their predecessors.
The microcontrollers are being used to help design engineers trim power requirements so more electronics can be powered by the 12-V battery system. Brushless motors are among the technologies being adopted to trim power consumption.
“These controllers let companies move to brushless motors, which are quieter, lighter, and more reliable than brushed or stepper motors,” said Willie Fitzgerald, Marketing Director for Microchip’s Automotive Products Group.
The 8-bit controllers can also help in the transition to LEDs, which have lower power consumption than conventional incandescent bulbs. The devices, which cost $1 or less, can be located near devices, offloading tasks from 32-bit CPUs.
“A large controller can manage a series of LEDs, but smaller controllers are often integrated at the LED, where it can operate efficiently without the overhead of having a big controller run things remotely,” said Greg Robinson, Marketing Manager with Microchip’s Security, Microcontroller & Technology Development Division.
For all these applications, network connectivity is also a critical element. LIN is commonly used with 8-bit devices, offering lower cost and enough capabilities to meet requirements. LIN’s usage is expanding rapidly.
“There’s really been a proliferation of LIN; it’s second in the number of nodes after CAN,” Fitzgerald said. “It’s got lower overhead and less wiring than CAN, so you can reduce weight and complexity.”
LIN’s simplicity is well suited for applications that require minimal bandwidth and location in remote areas where there is little room for electronics. It also requires little circuitry on the controllers.
“Our 8-pin part has a UART that is LIN compatible,” Robinson said. “That’s small enough to fit into small nodes on motors or close to LEDs.”
LIN also makes it possible for a single 8-bit chip to control multiple devices. For example, Microchip’s new devices have pulse-width-modulation (PWM) peripherals that have different time bases. Having PWMs with different time bases makes it possible to use one controller for both a mirror motor and an LED located in a door.
“With these PWMs, you can use different timers for LEDs and motors. Actions aren’t time critical; they sit on the LIN bus, which isn’t a time-critical bus,” Robinson said.