Data General NOVA ECLIPSE 6234 Service Manual page 44

Data General Corporation (DGC) has prepared this manual for use by DGC personnel and customers as a guide to the proper installation, operation, and
maintenance of DGC equipment and software. The drawings and specifications contained herein are the property of DGC and shall neither be reproduced in
whole or in part without DGC's prior written approval nor be implied to grant any license to make, use, or sell equipment manufactured in accordance herewith.
3.10.2 Recalibrate oeeration - The recalibrate operation positions the
drive read/write heads at cylinder zero. Recalibration is set up similar.
to a seek operation, except that the command and disk address registers
are loaded with the recalibrate command with no specified track address.
In a recalibrate operation, the microprocessor uses the home
transducer to locate track O.
To do this, the heads first move to the
home position (track 192 or less). The stepping motor then steps back
until reaching the phase position corresponding to track 0.
NOTE
If the drive is not accessed for two minutes, the micro-
processor turns off the stepping motor.
3.10.3 Write Operation - Once the heads are in position, the drive is
ready to accept a read or write command. A write command transfers
blocks of data (512 bytes/block) from the CPU memory to the disk via the
DCH.
To initiate a write operation, the CPU loads a wrfte command, the
head address, the starting sector address, and a number of sectors to be
transferred into registers on the CPU controller. The starting memory
address is also loaded to set up the transfer. The Busy flag is set
to one when the pulse is received by the microprocessor to start the •
write operation.
For Model 6234, the microprocessor now starts a DCH operation to
fill a buffer in the disk transfer logic with 512 bytes. Data words
move from the CPU to the CPU controller via an internal I/O bus and are
then stored in the sector buffer. When the buffer is full (512 bytes
transferred), the microprocessor sets up the write transfer. It places
first the current track address (from the preceding home transducer
command), the head address, and the sector address into a register.
When the selected sector approaches (i.e., the sector count from the
drive is one less than the selected sector), the microprocessor starts
the read/write operation.
The disk transfer logic first verifies that the address header is
correct by comparing the address stored in the controller PCB to the
word being read from the disk sector format. If an error is detected,
the microprocessor sets the Done flag, and the operation terminates.
The disk transfer logic now performs the next operation which is to
transfer the 512 bytes and develop a CRC. The logic first waits for a
specified time after the correct address header is read (splice zone),
then writes a preamble to be used by future read operations to sync the
read data clock. The 512 byte transfer is then performed and written to
the disk. During this transfer, the logic calculated a checkword and
writes this checkword to the disk after a transfer. A postamble is then
written to the disk to indicate to future read commands that the sector
ended.
015-000133
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