SPRUIZ1B July 2023 – August 2024 TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
The EMIF always drives the data bus to the previous write data value when the EMIF is idle. This feature is called data bus parking. Only when the EMIF issues a read command to the external memory does the EMIF stop driving the data bus. After the EMIF latches the last read data, the EMIF immediately parks the data bus again.
The one exception to this behavior occurs after performing an asynchronous read operation while the EMIF is in the self-refresh state. In this situation, the read operation is not followed by the EMIF parking the data bus. Instead, the EMIF tri-states the data bus. Therefore, it is not recommended to perform asynchronous read operations while the EMIF is in the self-refresh state, to prevent floating inputs on the data bus. External pull-ups, such as 10-kohm resistors, must be placed on the 16 EMIF data bus pins (that do not have internal pull-ups) if required to perform reads in this situation. The precise resistor value must be chosen so that the worst case combined off-state leakage currents do not cause the voltage levels on the associated pins to drop below the high-level input voltage requirement.
For information about the self-refresh state, see Section 11.2.5.7.