Acorn Computers Limited Winchester disk 110, Руководство по обслуживанию

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Each information transfer phase is as follows:
Command phase: allows the initiator to direct the subsequent action of the
target by transferring command bytes. The target asserts C/D and deasserts MSG
and I/O.
Status phase: allows the initiator to read the target's status information.
The target asserts C/D and I/O and deasserts MSG.
Data out phase: allows data to be transferred from initiator to target. The
target deasserts MSG, C/D and I/O.
Data in phase: allows data to be transferred from target to initiator. The
target asserts I/O and deasserts MSG and C/D.
Message out phase: not used by the system - available for future expansion.
Message in phase: allows the target to send a message byte to notify
completion of a command.
5.1.4 The reset condition
The reset condition is caused by the assertion of RST, and immediately clears
the bus and resets the system. Regardless of the prior bus phase, the bus
resets to the bus free phase. The Winchester controller reads the drive's
parameters off the disc.
Reset can occur at any time and takes precedence over all other phases and
conditions. In practice it occurs on power-up or when the BREAK key is
pressed.
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