TM4C1290NCPDT: The rise and fall time specification about input terminal (GPIO and UART)

Hello,

user5999038 said:

How much the rise time and fall time are allowed for UART (Rx) and GPIO (Input) ?

For a GPIO it would not make sense to characterize an input maximize rise time. The idea of the characterization of the output rise and fall times is to give a system designer an understanding of the worst case scenario for a signal controlled by the TM4C MCU to change. An external signal can behave however it wants and the system designer needs to take into account the rise or fall time from the output of the external device when determining how the TM4C MCU should react to the changing signal.

From a serial peripheral communication standpoint, the rise and fall times are governed by the selected data rate more than anything. For higher speed interfaces like SSI and I2C, some specifications are given to ensure the bus moves slowly enough to register data, but if the bus took longer to have signals rise and fall that just impacts the actual data rate of the transfer and again it is up to the system designer to account for that. In the event of a slave device responding to a provided clock signal too slowly, then the result would be missing data, but it would not be due to a characterized 'upper limit' for the rise and fall time but rather that the signal was not changed in time for the latching on a clock edge which will be consistently output as part of the data rate selected. Therefore it is the clock speed plus any specified valid/setup/hold times which governs the upper limits for proper operation with the clock speed being a variable based on system specific configuration.

In summary, the 'upper limit' of rise/fall times for an external signal that is input into the TM4C is not a specification that can be characterized universally as it is application and system specific and needs to be determined by the system designer based on expected performance.

Best Regards,

Ralph Jacobi