Now that magnetoresistive RAM has been on the market for several months, demand is growing for system-on-chip (SoC) products that contain embedded MRAM. There are many advantages to having an embedded MRAM integrated as part of an overall system for future microcontroller units (MCUs). MRAM's ability to access memory in bytes allows great flexibility with memory partitions. Any section of the memory can be decoded as program memory or data storage. This flexible decoding or memory partitioning can even occur on-the-fly.
An intelligent automotive airbag application can serve as an example. An airbag module is installed into a new car at the assembly plant. When the car's ignition is started for the first time, the airbag module can gather baseline information from the car's other systems. The information collected can be the model and year of the car, the type of seats it has, the type of steering wheel, and the number and location of the airbags and sensors. This is all baseline information that the MCU collects so that it can perform a self-configuration. This is necessary because a single airbag module can be used in many car models with a varying number of airbags and sensors, and different types of body designs, seats and steering wheels.
The configuration data can be stored in a separate partition of the MRAM with a write-protect option so this critical information does not accidentally get overwritten. Other information can come from crash-detect accelerometers, passenger weight transducers and seat position data. The configuration data can change from one moment to the next, and it can be stored in a second MRAM partition that does not have the write-protect option so that the data can be overwritten regularly with updated information as the car is being driven.
The main airbag application program memory, which tends to require the most memory, can be stored in a third partition of the MRAM. The third partition can feature a security option so the program cannot be overwritten because of an MCU runaway fault condition, and the memory contents cannot be read or altered by unauthorized outside tampering.
There are a lot of opportunities for improvement, however. Clever techniques used to minimize the power consumption of the MRAM analog circuitry enable efficient battery use.
MRAM logic-0 and -1 states are interpreted by the sense amplifier, which detects a change in the bit resistance from one state to another. If the resistance of the logic-1 state can be widely separated from the resistance of the logic-0 state, it would allow the sense amp to read the bit more quickly. This will enhance the speed performance by reducing the access time.
Improvements in MRAM will help widen the spectrum of potential applications, ensuring a greater push into the embedded-microcontroller market. With the enhanced feature set of MRAM, we can expect to see MRAM-based MCU designs going into many unique and interesting applications.
Lam Ta (firstname.lastname@example.org) is microcontroller technologist and Tom Lee (email@example.com) is in MRAM product engineering in the Transportation and Standard Products Group, Microcontroller Division, of Freescale Semiconductor Inc. (Austin, Texas).