Automotive Electronics Design Fundamentals by Najamuz Zaman

Author:Najamuz Zaman
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

The specific load in this topology could be a relay, a solenoid, a heater or a lamp. For the sake of clarity, all other interfaces are also shown, mainly battery transfer electronic switch S2, safety and protection block, battery and fuse. Software task ‘status’ has configured a single bit to read as an status in an additional port namely Digital Input (D.I) to check the status of the high side driver switch. Software tasks ‘status’ require an extra hardware to monitor the switch operational condition, which is extremely important in many critical real time systems.

The battery electronic switch S2 as explained in Sect. 3.4 is primarily used to switch the battery power to the appropriate load by utilizing the microcontroller digital output (D.O.), thereby executing the software task ‘BattSwitch’. This is the first task the software has to do before it attempts to turn on the intended load. Please bear in mind that at this time load is ready to get energized but is still not energized yet, because path to ground through high-side driver is not complete. Nonetheless the path to ground may only be completed when the high-side driver is turned on. This happens when the software task ‘Toggle’ is executed by sending microcontroller digital output port (D.O.) to logic-zero or logic-one (depending upon the hardware design). The vehicle-specific function load, now, eventually gets energized at this point.

The question is how the microcontroller software would know that the operation had successfully executed? In order to validate the correct switching operations executed by the software it is essential to monitor the switch-status to detect any unsuccessful operation. To achieve the capability of switch-status monitoring, additional hardware must be added to the high-side driver to get to the status-line output.

The status-line output is then translated to the desired digital input level where it is read by the microcontroller to determine if the intended switching operation was indeed successful. The software task ‘Status’ gets executed to read the feedback status from the high-side driver feedback loop by the application code to also determine if the operation was successful.

If for any reason the switch status does not come out ‘true’, meaning, the operation was not performed as intended, then the operational code logs the fault and stores it as a diagnostics trouble code.

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