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Section IV
12606B
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--'SECTOR 00000001 SECTOR 0000001
~
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1
...-iSECTOR 10110011 SECTOR 1011010 ~
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I'~'--~------~------~U~-----
SC
SCP
FF
n
n
IL,
"
I
J
SCO
FF
"
"
SCI FF
,
I"
SC2 FF
,
,
SC3
FF
,
,
.
,
SC4 FF
I
,
SC5
FF
,
,
SC6 FF
,
.
,
NOTE:
NOT TO SCALE HORIZONTALLY.
2032-3
Figure 4-2. Sector Counter Timing Chart
write heads. Consequently, it is too late in the current disc
revolution to start a write or read operation in the sector
indicated by the sector select register (bits 14 through 8 of
the status word). If an attempt is made to start such an
operation, it will not begin until two disc revolutions later.
During these revolutions the Run FF remains set. The
set-side output of the Run FF is furnished to diode CR1,
which forms one input of a 2-input "or" gate made up of
CR1, CR2, and the input circuit of "and" gate MC37B. If,
during the 2-revolution waiting period, an LIA/B instruc-
tion acquires the disc status word, "and" gate MC37B
forwards the output of the CR1-CR2 "or" gate to lOBO
line 0 as bit 0 of the disc status word. Since the Run FF is
set at this time, bit 0 of the status word will be logic 1,
indicating that the disc is busy. (Refer to table 3-2_)
4-42.
It
has been seen that after poweJ; is applied to the
computer and disc, the. trailing edge of the first "not" SC
pulse after the first "not" TO pulse sets the SCP FF. With
this flip-flop set, the second "not" SC pulse (inverted)
clears the word counter and EOS FF on the command card
through "nand" gates MC54E and MC64E. A-Iso, "nand"
gate MC34B sets the STR and WRD, FFs, and clears the bit
counter. (Gate MC44A, used in clearing the bit counter,
functions as a negative-logic "nor" gate.)
4-43.
To summarize the initial condition of the data
card and command card after power is applied to the
4-6
computer and the disc, flip-flops and registers are in the
following condition:
a. The Control Bit FF is reset.
b. The Flag FF is reset.
c. The Run FF is reset.
d. The SAC FF is reset.
e. The ABS FF is set.
f. The sector counter contains the address of the next
disc sector, and is running.
g. The word counter is reset and not running.
h. The EOS FF is reset.
i.
The bit counter is reset and not running.
j.
The STR FF is set.
k.
The WRD FF is set.
1.
The RP FF is set.
m. The TOS FF is set.
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