The PIO and UDMA settings for the drive are controlled with the ISD-300A1's EEPROM contents. Address 0x0C of the EEPROM holds the UDMA settings. If UDMA is enabled in the EEPROM and is supported by the drive, the 300A1 will run at the highest UDMA mode specified in the EEPROM that the drive supports. If UDMA is disabled, then the 300A1 will use the highest PIO mode that the drive supports.
Please note that the ISD-300A1 is obsolete and the functional replacement is AT2LP. All the related collaterals can be found here