Data Rate Delay1 Mps 83.00500 Kps 125.00300 Kps 125.00250 Kps 125.00DRATESEL Data Rate SelectThese bits select the data transfer rate. Reset clears these two bits. Data rates get se-lected as follows:Bit Data Rate (bits/second)1 0 MFM FM0 0 500 2500 1 300 1501 0 250 1251 1 1000 Not definedFirmware Download (AHA-1740/1744 Only)The AHA-1740A/1742A permanently stores both Standard and Enhanced Mode firm-ware in an EPROM. A microcode upgrade consists of replacing that EPROM with an-other, and is seldom required. Please contact Adaptec for further information.The AHA-1740/1744 permanently stores both Standard and Enhanced Mode firm-ware in an E2PROM.The local processor will download the firmware from EEPROM and will run fromRAM. In order to promote maximum data integrity, the firmware calculates check-sums for itself while not executing commands. The firmware is interrupt driven byevents on the host and SCSI side.The firmware is programmed into the EEPROM by setting the Enable Prom Writebit in the PORTPH register. When this is done, reads will come from the RAM andwrites will go to the EEPROM. The firmware is enabled to reprogram when theCONFIG bit in PORTADDR is set and the firmware download command is given.The AHA-1740 INTERFACE bit in PORTADDR indicates which code to program.Provision is also made for loading of new firmware without programming. This defini-tion is in the AHA-1740 Configuration document.adaptec AHA-1740A/1742A/17444-26
