Write Mode Sensing - IBM 5114 Maintenance Information Manual

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The data rate in a write operation is 24K bytes/second.
The write operation starts when the system sends the
START WRITE command to the adapter. This command
comes on the 'bus out' line, diskette control byte, bit O.
When the adapter senses that this bit is turned on, it
sends a signal to the write control block. This block
raises the 'interrupt request 2' line. This causes the
system to send the first byte of data to the buffer and
reset the interrupt request.
Now the buffer transfers the byte of data to the write
serializer and raises the 'interrupt request 2' line to
obtain the next byte of data.
The first bytes (6 in FM, 12 in M FM) are all 0' s. This is
the sync field. After the sync field is written, the system
sends the WRITE AM 'command on the 'bus out' Hne,
diskette control byte, bit 6. This sets the 'write AM' the
latch in the write control block which brings up the
'write gate' line and turns on the' erase gate' latch.
Turning on the 'erase gate' with the WRITE AM
command provides the necessary delay at the beginning
of the write operation before the tunnel erase operation
begins (544 microseconds). The oscillator provides the
correct clock pulses for the address mark and the data.
When the address mark is written, the system resets
the 'write AM' latch and starts sending data. The write
serializer takes a byte of data and sends it to the write
generator a bit at a time. It also sends the data a bit at
a time to the eRe generator.
After all the data is written, the system issues, a WRITE
eRe command over the 'bus out' line, diskette control
byte, bit 5. This command is decoded and the 'write
eRe' line causes the 2 eRe bytes to be written serially
from the eRe generator to the diskette.
While writing the eRe, the adapter still interrupts the
system. The system has to service these interrupts by
sending dummy data.
When the eRe information is written, the system issues
a RESET WRITE command over the 'bus out' line,
a.skette control byte, bit 7. This stops the write
operation.
Because the erase heads are physically located behind
the read/write heads, the tunnel erase operation has not
been completed at this time. An erase counter provides
a drop out delay to the erase heads of 544
microseconds after the RESET WRITE command has
been received.
The system now issues a START READ command over
the 'bus out' line, diskette control byte, bit 1. This puts
the adapter in read mode. The adapter now reads and
sends all of the data just written to the system. The
data is compared bit for bit in the system for validity.
This is the verify read operation.
WRITE MODE SENSING
During a write operation, the system is sensing the
condition of the adapter over the 'bus in' line by
sampling the diskette sense byte. The bits of the
diskette sense byte are used to inform the system of
the condition of several latches during the write
operation. (See Diskette Sense under Adapter Commands
in this section.)
Operations 3-35