Add safety-critical features to control applications with 8-bit PICs

February 26, 2014 // By Graham Prophet
Microchip has added low pin-count, general-purpose 8-bit PIC MCUs that have features addressing safety-critical applications: a 24-bit Signal Measurement Timer (SMT) enables more precise and accurate measurements, and these PICs gain hardware Zero Cross Detect (ZCD) for robust operation, plus fault-detecting hardware including a Hardware Limit Timer

Low pin-count PIC16(L)F161X devices add to Microchip’s Core Independent Peripherals (CIP), which off-load timing-critical and core-intensive tasks from the CPU. These devices integrate fault-detecting hardware features for safety-critical applications. The Windowed Watchdog Timer (WWDT) monitors proper software operation within predefined limits. The Cyclic Redundancy Check with Memory Scan (CRC/SCAN) detects and scans memory for corrupted data. This family also includes a Hardware Limit Timer (HLT), which detects hardware fault conditions, including stall and stop, to simplify closed-loop-control applications. These peripherals make it easier for designers to implement safety standards such as UL & class B, or fail-safe operation.

In addition to the HLT, the PIC16(L)F161X features the 24-bit Signal Measurement Timer (SMT). The SMT performs high-resolution measurements of any digital signal, in hardware, resulting in more precise and accurate measurements. This is suited to speed control, range finding and RPM indicators. Both timers are designed to reduce design complexity, by eliminating the need for additional code and external components. These are also the first PIC MCUs to offer hardware Zero Cross Detect (ZCD), to simplify TRIAC control and increase system robustness by minimising the EMI caused by switching transients. A Complementary Waveform Generator (CWG), comparators, 10-bit ADC, 8-bit DAC and Capture/Compare PWM are also integrated, to enable design flexibility and overall cost reduction. The CWG can generate complementary waveforms with fine control of key parameters, such as polarity, dead-band and emergency-shutdown states. It provides a cost-effective solution for half-bridge and full-bridge drive control, which saves both board space and component cost when driving FETs in motor-control and power-conversion applications. All of these features are provided in small-form-factor packages, ranging from 8 to 14 pins.

Microchip asserts that coding and additional hardware associated with implementing safety and control in an embedded system can be reduced by exploiting these integrated hardware features. PIC12(L)F1612 MCUs come in 8-pin PDIP, SOIC, and 3 x 3 mm DFN and UDFN packages. The PIC16(L)F1613 MCUscome in 14-pin PDIP, SOIC, TSSOP, and 4 x 4 mm UQFN and QFN packages. More at; www.microchip.com/get/VDLM

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