Texas Instruments MSP430 is one of the most popular 16-bit microcontrollers. Its low power and high performance make it ideal for a range of applications including meter reading. The 25MHz MSP430F6736 (Fig. 1) targets this space although its mix of analog-to-digital converters (ADC) make it applicable to other applications as well.
The MSP30F6736 handles not only sensing chores but also display chores as well. In fact, it is designed to work with large LCD displays with many segments. This type of display is necessary in many regions where more complex characters are required.
The chip has a 10-bit, 8-channel, 200 Ksample/s, successive-approximation-register (SAR) ADC. Six channels are external while two are internal including temperature sensor support. A SAR ADC is faster than the Sigma-Delta ADCs.
There also has three 24-bit, Sigma-Delta ADCs. The ADC runs off a 1 MHz clock. The inputs have programmable gain amplifiers. These ADCs meets class 0.1 meters and exceeds IEC62053/ANSI C12.20 requirements.
The 24-bit ADCs are normally used for meter reading chores. Having three 24-bit ADCs allows simultaneous conversion. A muxed approach would require sequential readings.
The microcontroller family supports up to 128 Kbytes of flash program memory and 8 Kbytes of SRAM. There is a 32-bit hardware multiplier and a CRC16 accelerator.
Other peripherals include:
- 320 segment LCD drive with 8-mux mode support
- Three Enhanced Universal Serial Communication Interfaces (USCI) with IrDA support
- Three Enhanced Universal Serial Communication Interfaces (USCI) with I2C support
- Three 16-bit timers. Each has two capture/compare registers
- One 16-bit timer with three capture/compare registers
- 3 DMA channels
- Password-protected real time clock
The USCI interfaces with IrDA support also have auto-baudrate detection. The USCI with I2C support can handle multi-slave addresses. All can handle SPI interfaces.
The chip also has a password-protected real-time clock with crystal offset calibration and temperature compensation. This is paired with data that would be acquired using the Sigma-Delta ADCs to prevent corruption or aliasing of information.
The chip has a range of low power modes. A separate battery backup supply handles the low frequency oscillator, real time clock and backup memory (4 words).
The Single-phase Meter EVM evaluation module (Fig. 2) provides an easy way to check out the MSP430F6736 in a meter reading environment. The EVM has inputs for voltage and current. The third input is for anti-tampering. There is an on-board LCD display as well.
Pricing starts under $2. The chip comes in 80- and 100-pin LQFP packages.