AM6421 datasheet(105/237 Pages) TI

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Table 6-78. Unused Balls Specific Connection Requirements (continued)

BALL NUMBER

BALL NAME

CONNECTION REQUIREMENTS

T13

W16

W17

Y15

Y16

AA16

AA17

SERDES0_REXT

SERDES0_REFCLK0N

SERDES0_REFCLK0P

SERDES0_RX0_N

SERDES0_RX0_P

SERDES0_TX0_N

SERDES0_TX0_P

Leave unconnected.

Note: The SERDES0_REXT pin can only be left unconnected when

VDDA_0P85_SERDES0, VDDA_0P85_SERDES0_C, and

VDDA_1P8_SERDES0 are connected to VSS. The

SERDES0_REXT pin must be connected to VSS through the

appropriate external resistor when VDDA_0P85_SERDES0,

VDDA_0P85_SERDES0_C, and VDDA_1P8_SERDES0 are

connected to a power source.

(1)

To determine which power supply is associated with any IO refer to Section 6.2, Pin Attributes.

Table 6-79. Reserved Balls Specific Connection Requirements

BALL NUMBER

CONNECTION REQUIREMENTS

D21, F12, F17, G13, H16, K1, K2, V16, W15

These balls must be left unconnected.

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.

Note

All other unused signal balls without a Pad Configuration Register can be left unconnected.

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SPRSP56 – JANUARY 2021

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