AM6548, AM6528, AM6526
ZHCSLA7B –DECEMBER 2019 –REVISED JUNE 2021
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Note
All other unused signal balls with a Pad Configuration Register can be left unconnected with their
multiplexing mode set to GPIO input and internal pulldown resistor enabled.
Unused balls are defined as those which only connect to a PCB solder pad. This is the only use case
where internal pull resistors are allowed as the only source/sink to hold a valid logic level.
Any balls connected to a via, test point, or PCB trace are considered used and must not depend on
the internal pull resistor to hold a valid logic level.
Internal pull resistors are weak and may not source enough current to maintain a valid logic level for
some operating conditions. This may be the case when connected to components with leakage to the
opposite logic level, or when external noise sources couple to signal traces attached to balls which are
only pulled to a valid logic level by the internal resistor. Therefore, external pull resistors may be
required to hold a valid logic level on balls with external connections.
If balls are allowed to float between valid logic levels, the input buffer may enter a high-current state
which could damage the IO cell.
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