Other Registers In Disk Operations - Commodore Amiga Hardware Reference Manual

If you have too little memory for track buffering (or for some other reason decide not to
read a whole track at once), the disk hardware supports a limited set of sector-searching
facilities. There is a register that may be polled to examine the disk input stream.
There is a hardware bug that causes the last three bits of data sent to the disk to be
lost. Also, the last word in a disk-read DMA operation may not come in (that is, one
less word may be read than you asked for).
OTHER REGISTERS IN DISK OPERATIONS
A number of other registers are also associated with disk operations, as specified below.
DSKBYTR - Disk Data Byte and Status Read
This register is the disk-microprocessor data buffer. In read mode, data from the disk is
loaded into this register one byte at a time. As each byte is received into the register,
the BYTEREADY bit is set true. BYTEREADY is cleared each time the DSKBYTR
register is read.
DSKBYTR is the register normally used by system software to synchronize the processor
to the disk rotation before issuing a read or write under DMA control. The bits are
shown in table 8-8.
232 Interface Hardware