Why to use a System Basis Chip

 In an usual embedded product we see following set up . Processing logic runs inside MCU and both sensors and actuators are connected to it . MCU takes input from sensor and based on that input processing logic decide how to control actuators . Same like the example given in here . 

During the life time of the product , MCU could fail due to several reasons Ex : High voltage or current , static , reset due to internal logic state etc. The example here is a safety critical scenario. As in case of a fire if water is not sprinkled in time it may lead to loss of human life. So in such a safety critical scenario , how can we ensure higher reliability. As it is possible MCU failed to deliver when needed. 

 

 

         This is where we use SBC . It continuously monitor MCU health and based on that decide to take over the control of actuator . It does not have the processing logic to decide actuator state based on sensor input. So SBC push actuator to a default safe state. This safe state is decided as part of system design. For example here start high pressure pump to sprinkle water could be a safe state. So regardless of whether there is fire or not , if SBC detect MCU failure , then it start pressure pump. So in any case risk is averted. Now one can argue that , it is possible both MCU and SBC failed. Yes it is possible, after all they are electronics chips. So we can not ensure 100% reliability , but we increased the reliability and decreased the probability of failure by using SBC.

 

What is System Basis Chip

• System Basis Chip in short SBC, is a chip used in safety critical systems to work as a guardian to MCU . Below picture is an example use of NXP FS6500 SBC .
  

 

• It can be seen in above picture , SBC(FS6500) is connected to a Microcontroller Unit (MCU)
• MCU is the chip which contains the business logic of the product. In other words , the application functionalities for which the product is developed , lies inside MCU .
• Example : Assume we are developing an embedded product which will monitor a smoke sensor and control a water pressure pump to sprinke water in case smoke is detected. The logic which conclude the pump state (ON/OFF) based on smoke sensor input is flashed as a firmware on to MCU . Both smoke sensor and pump are connected to MCU , to give input and to get controlled .
• SBC controls power , data , reset , CAN , ADC , DEBUG, IO and some control outs to MCU
• SBC is like an umbrella to MCU . It takes over control from MCU in certain predefined scenarios.
• It might have built in test  to continuously monitor its interfaces and internal circuit logic.
• NXP FS6500 has configurable Fail-safe/Fail silent safety behavior and features, with two fail-safe outputs, it has capability to support till ASIL D.

To know why we should use SBC in a product read : This Blog