82077AA-1/SL-l has the capability to support up to a total of four drives. Most PC systems today have at least one floppy disk drive. This leaves the possibility of installing up to three tape drives.
The following describes a way to configure the floppy disk controller in a multiple tape drive environment. This also depends on whether the system manufacturer wishes to leave certain drive slots fixed for tape drives or variable by the user.
All tape drives are variable - If the drives chosen as tape drives are variable then the configuration mechanism used is strictly software. After strapping PLL0 high the bits TDR[0:l] can be programmed during initialization for various drives that can be selected as tape drives. It should be noted that in this case drive 0 cannot be selected as one of the tape drives.
Combination of fixed variable tape drives - If any drive can be determined to be fixed then either the motor enable pin or the drive select pin of that particular drive can be used to drive PLL0 to GND when selected. Fig.1 and Fig.2 show two scenarios where drives that are fixed for tape drive use their motor enable or drive select signals to drive PLLO to GND.
Fig. 3 shows by using jumpers flexibility can be incorporated in the system and the drive 5 to be fixed for tape drives can be left to the user.