In such a case, the ISD-300 logic will first check to see that the drive supports UDMA. If it does, then the ISD-300 will negotiate the highest supported UDMA mode allowed by the EEPROM data. If UDMA is not supported by the device, then the ISD-300 will automatically configure itself to whatever override value was entered in the EEPROM data.
Please note that the ISD-300A1 is obsolete and the functional replacement is AT2LP. All the related collaterals of AT2LP can be found in the link here