During drive initialization, after resetting the drive, if the drive supports UDMA mode, then the transfer mode is set to UDMA. Else, the highest PIO mode is enabled. Enabling the correct mode is done by the following procedure.
First of all, the Sector Count register is written with the 'transfer mode' which has to be set. Then 0x03 is written to the Feature register to indicate that this is a 'set tansfer mode' command. Finally, the command register is written with the 'set feature' command which causes the execution of the command.
The AT2LP is a fixed-function part, so there is no software or firmware that can be rewritten to change the behavior of the chip.