Parameter Storage in EEPROM (Non-volatile Parameter Storage)
This is holding user settings such as speed, torque, ramp time and protection threshold in memory that is not erased when power is cut. This way the device runs with its last settings every time it is switched on. The write count of non-volatile memory cells is limited; for this reason settings are saved not continuously, but only when they change.
There are three points that are watched in practice.
- Write endurance: the non-volatile memory cells inside a microcontroller withstand, according to manufacturer data, typically on the order of hundreds of thousands of write cycles. Software that writes a record in every control loop uses up this limit far sooner than expected.
- Integrity: if power is cut during writing, a half-written parameter block may remain. For this reason a checksum value is added to the block; if the checksum does not hold at power-up, default values are loaded.
- Version field: a structure version is written at the start of the parameter block; during a software update this is how it is understood how the old record is to be interpreted.
From the user's point of view the result is this: the device's settings are preserved even if power is cut, but in case of unexpected behaviour there is a return-to-default-settings function so that the settings can be brought back to a known starting point. The range within which the settings are defined in the manual is also consistent with the limits in this memory.
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