Write Signal on Disk II Question

["Bryan Parkoff" <nospam@nospam.com>]

    I study Logic Sequence ROM.  It does not make sense when I look at Write 
Sequence table.  I decide to store $FF on data bus before data bus.  Load 
switch transfers $FF from data bus to data register.  Shift switch continues 
the state sequence to shift left one bit into QA like as MSB.  QA is always 
set for all 8 bits.  The Write Signal toggles between two loops while QA is 
set.  It looks like this below.

QA   Data Register   Write Signal
0    11111111   0   Load $FF
1    11111110   1   Shift 1st bit
1    11111100   0   Shift 2nd bit
1    11111000   1   Shift 3rd bit
1    11110000   0   Shift 4th bit
1    11100000   1   Shift 5th bit
1    11000000   0   Shift 6th bit
1    10000000   1   Shift 7th bit
1    00000000   0   Shift 8th bit

    QA is ideal to show digital bit stream.  Write Signal is analog bit 
stream.  It controls the current in the coil of the read/write head.  Also, 
it has second head like as erase head..  The high/low state of the Write 
Signal determines the direction of the magnetic field set up in the 
read/write head.  Please explain more about the field reversal and the lack 
of field reversal why Write Signal is required to toggle while QA is always 
set for all 8 digital bits.
    I may be curious to see if I can simulate mangetic field to show field 
reversal or lack of field reversal.  It shows the same thing like Read 
Pulse.

Bryan Parkoff