SPRAD21E May 2023 – February 2024 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP , AM62A3 , AM62A3-Q1 , AM62A7 , AM62A7-Q1 , AM62P , AM62P-Q1
In the SK, the boot mode pins BOOTMODE [15:00] are asserted through two buffers (isolation buffers). The buffers ensure that SYSBOOT pulls (boot mode configured using resistors) are controlling the level of the signals when the boot mode signals are being latched (around the PORz_OUT rising edge) by the processor. Since boot mode signals are often used for other functions after processor power-up and are connected to attached devices or peripherals, boot mode configuration resistors need to be isolated from other connected peripherals so that those peripherals do not conflict with the intended boot mode configuration (signal levels).
The buffers are enabled when PORz_OUT is driven low by the processor. After PORz_OUT goes high, the buffer outputs are Hi-Z so the signals are not pulled or influenced by the boot mode resistors.
For optimizing the design (including BOM), these buffers can be optimized or deleted depending on the use case. The boot mode pull resistors value can be selected so that they do not affect the operation of attach devices.