ACT apricot - Page 99

FLOPPY DISK INTERFACE
On detecting the Index Pulse, the FDC transfers the byte
within the Data Register to an encoding circuit and issues
another DMA request to the lOP. The lOP responds by
writing the next byte to the Data Register and the process is
repeated. The encoding circuit converts the byte into MFM
data and writes the data onto the disk.
This process continues until the FDC detects the next
Index Pulse, which causes the FDC to generate an interrupt
request on the INTRQ output. The interrupt request again
has the same functions as described before; i.e. informs the
lOP to terminate the DMA transfer routine and also
interrupts the CPU, via the Interrupt Controller. Resetting
the INTRQ output is achieved by reading the Status
Register or issuing a command to the FDC.