Microchip Technology Inc. announced the PIC32 family of 32-bit microcontrollers (MCUs). The PIC32 family adds more performance and more memory while maintaining pin, peripheral and software compatibility with Microchip’s 16-bit MCU/DSC families. To further ease migration and protect tool investments, the PIC32 family is fully supported by Microchip’s free MPLAB^® Integrated Development Environment (IDE). The MPLAB IDE offers unprecedented compatibility by supporting Microchip’s complete portfolio of 8-, 16- and 32-bit devices.

“As a world leader in embedded-control solutions, Microchip is introducing the PIC32 family to build on the success of our vast 8- and 16-bit portfolio and offer customers a seamless migration path that bridges product families,” said Ganesh Moorthy, executive vice president of Microchip. “We provide designers with the most compatible environment in the industry for developing systems with 8-, 16-, and 32-bit MCUs!”

Consumers’ desire for ever-more engaging end products is driving system requirements for increased memory capacity, performance and functionality. Launching with seven general-purpose members, the PIC32 family operates at up to 72 MHz and offers ample code- and data-space capabilities with up to 512 KB Flash and 32 KB RAM. The PIC32 family also includes a rich set of integrated peripherals, significantly reducing total design complexity and cost. Examples include a variety of communication peripherals, a 16-bit Parallel Master Port supporting additional memory and displays, as well as a single-supply on-chip voltage regulator.

“Microchip brings a new perspective to the ever-growing 32-bit microcontroller market, born of their tremendous success in the 8-bit market,” said Tom Starnes, processor analyst at semiconductor market research firm Objective Analysis. “The peripheral-compatible PIC32 family should bring comfort to Microchip’s customers, knowing that the headroom is available as their applications evolve.”

The PIC32 family is based on the industry-standard MIPS32^® architecture, with its leading combination of high performance, low power consumption, fast interrupt response and extensive industry tool support. The high-performance MIPS32 M4K^® core can achieve best-in-class 1.5 DMIPS/MHz operation, due to its efficient instruction-set architecture, 5-stage pipeline, hardware multiply/accumulate unit and up to 8 sets of 32 core registers. To reduce system cost, the PIC32 supports MIPS16e™ 16 bit ISA—enabling code-size reductions of up to 40%.

“In the hands of the architects at Microchip, the MIPS architecture will do well in 32-bit MCUs,” said Max Baron, principal analyst at In-Stat. “Microchip gets a great architecture, while MIPS gets to be part of a series of MCUs from a company that is very successful in the MCU market. It’s a win-win for both companies.”

Wheatstone bridge

A Wheatstone bridge is a measuring instrument invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer except that in potentiometer circuits the meter used is a sensitive galvanometer.

Wheatstone's bridge circuit diagram.

In the circuit at right, R_x is the unknown resistance to be measured; R₁, R₂ and R₃ are resistors of known resistance and the resistance of R₂ is adjustable. If the ratio of the two resistances in the known leg (R₂ / R₁) is equal to the ratio of the two in the unknown leg (R_x / R₃), then the voltage between the two midpoints will be zero and no current will flow between the midpoints. R₂ is varied until this condition is reached. The current direction indicates if R₂ is too high or too low.

Detecting zero current can be done to extremely high accuracy (see Galvanometer). Therefore, if R₁, R₂ and R₃ are known to high precision, then R_x can be measured to high precision. Very small changes in R_x disrupt the balance and are readily detected.

If the bridge is balanced, which means that the current through the galvanometer R_g is equal to zero, the equivalent resistance of the circuit between the source voltage terminals is:

R₁ + R₂ in parallel with R₃ + R_x

Alternatively, if R₁, R₂, and R₃ are known, but R₂ is not adjustable, the voltage or current flow through the meter can be used to calculate the value of R_x, using Kirchhoff's circuit laws (also known as Kirchhoff's rules). This setup is frequently used in strain gauge and Resistance Temperature Detector measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage.

Derivation

First, we can use the first Kirchhoff rule to find the currents in junctions B and D:

Then, we use Kirchhoff's second rule for finding the voltage in the loops ABD and BCD:

The bridge is balanced and I_g = 0, so we can rewrite the second set of equations:

Then, we divide the equations and rearrange them, giving:

From the first rule, we know that I₃ = I_x and I₁ = I₂. The desired value of R_x is now known to be given as:

If all four resistor values and the supply voltage (V_s) are known, the voltage across the bridge (V) can be found by working out the voltage from each potential divider and subtracting one from the other. The equation for this is:

This can be simplified to:

The Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate. Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of combustible gases in a sample, with an explosimeter. The Kelvin Double bridge was one specially adapted for measuring very low resistances. This was invented in 1861 by William Thomson, Lord Kelvin.

The concept was extended to alternating current measurements by James Clerk Maxwell in 1865 and further improved by Alan Blumlein in about 1926.

External links

• efunda Wheatstone article