UART16750

Hello, I am trying to use this core in a Spartan 6 connected to a Arm processor. In order to get the timing of the link between the ARM processor and the Uart16750 core I wanted to know what manufacture did you base your timing interface of the Uart16750 off of?

Currently I am trying to use the TI TL16c750 datasheet as a reference for the timing interface to the Uart16750 core. I wrote a simple test that writes to the SCR scratch register, then clears the data bus, then reads the SCR scratch register and verifies it is the data we wrote to it. This works for a couple of writes and reads but then fails randomly. When it fails it reads back the data that was previously written to the SCR register and not the data that was just written to it. This is what is leading me to believe I have a timing issue and wanted to see if you can point me to the correct datasheet I should be using for the timing values of the Uart16750 interface.