SPRADO8 March 2025 AM62L
The processor family supports two different BOOTMODE pin mapping options, as shown below:
The reduced pincount boot mode mapping offers the advantage of requiring less bootstrap pins which can translate to fewer pullup or pulldown components required. The reduced pincount boot mode comes at the cost of making fewer boot mode options pin selectable.
However, two of the boot mode options that are selectable from the BOOTMODE Pin Mapping (Reduced) table can be customized to any of the full 16-bit options by programming a new value into EFUSE. The EFUSE values are also protected using SECDED error correcting encoding scheme; 22 fuse bits are used to encode the 16-bit boot mode value.
To realize the desired reduction in pullup or pulldown components required, the input buffers for pins BOOTMODE[11:0] are disabled during POR unless BOOTMODE[15:14] are '00'. Disabling the buffers avoids power consumption due to floating inputs on these pins if the reduced pincount option is used.
When dip switches are used for configuring the boot, use a resistor divider ratio of 470Ω (pullup) and 47kΩ (pulldown) for improved noise performance.
When the boot mode is configured using only resistors, a standard resistor (same value for pullup and pulldown) value. For example, a 10kΩ or similar resistor can be used since either the pullup or pulldown is populated.
The recommendation is to connect pullup or pulldown to boot mode pins marked as Reserved or not used.
Add a provision for pullup and pulldown for all the boot mode pins that have configuration capability for debugging, design flexibility, and future enhancement. Populate either pullup or pulldown for each boot mode pins. Direct connection of boot mode pins to ground or IO supply rail is not recommended or allowed since IOs have alternate configuration and, intentionally or unintentionally, are configured as output by the software.
Consider that the boot mode input pins are not fail-safe when boot mode configurations are driven from an external input or a base board.
Based on the application requirement, a buffer that is driven only when reset (PORz) is asserted (low) is used to present the boot configuration to the processor.
If the boot mode pins are configured as an output during normal operation, then a series resistor (approximately 1kΩ) is recommended at the output of the buffers. For more information, see the processor-specific EVM for implementation.