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Functional Description
7936 and 7937
MNEMONIC
SMPN,
SMPP
SOS-L
SOSEN-H
SPOSNS-L
5-64
SIGNAL
Sampled
Servo,
Negative,
Positive
Start of
Sector**
Start of
Sector
Enable
Speed Sense
Table 5-1. List of Mnemonics (17 of 23)
SOURCE
IBII
A2
IJA1
~A3
DESCRIPTION
SAMPLED SERVO AGC AMPLIFIER dif-
ferential output.
The amplifier input is
Read/Write Data signal OX, OY, gated by the
SAMPLED SERVO SWITCH to allow only
the sampled servo information prerecorded
between data sectors to reach the amplifier.
SMPN
and
SMPP
are connected to the input
of the SAMPLED SERVO FILTER in servo
PCA-Ai.
BUFFER
output
to
READ/WRITE
CONTROLLER.
SOS-L,
derived from servo
system
OSOS-L, OSOS-H,
goes high for the
duration of the sampled servo field. The fall-
ing and rising edges of the signal determine
the beginning and end of the writeable data
field. The signal is used in the write chain as a
Disc Data Bus handshake line. The controller
uses
SOS-L
to initiate a data transfer across
the bus. Since
SOS-L
is generated, not only
for sectors which will be transferred, but for
all sectors, the controller also uses
SOS-L
to
count sectors and keep track of rotational
position.
SOS-L
can be monitored at pin
13
of the
read/write test point PCA.
SOS-L
is connected to the READ/WRITE
CONTROLLER in read/write PCA-A2 and
the DMA/ECC in controller PCA-A6.
SERVO
CONTROLLER
output
to
SAMPLED SERVO TIMING.
SOSEN-H
controls the generation of Start of Sector
SOS-L.
Speed
sensor
output
to
SER VO
CONTROLLER.
SPOSNS
is used at power
on to determine when the spindle is rotating
fast enough to allow the heads to be moved
away from the landing zone.
SPOSNS
is
connected
to
the
SERVO
CONTROLLER in servo PCA-A 1 via power
power distribution PCA-A5 and read/write
PCA-AI.
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