Radio Shack TRS-80 Service Manual page 106

DATA RECORDING
Referring to Figure 4, it can be seen that the Write Elec·
tronics consists of a Write/Erase Current Source and Write
Waveform Generntor, Eriil5ill Current Source, and Trim Ernse
Control Logic.
The read/write winding on rhe magnetic head is center·
tapped. During
a
write operation. current from rhe Write
Current Source flows in alternate halves of the winding
under control of the Write Waveform Generator.
Before recording can begin, certain conditions must be
satisfied. The conditions required for recording (i.e., unit
ready) must be established by the user system as follows:
III
Drive
speed
stabilization. This condition will
exist 250 mSec after starting the drive motor.
(2)
Subsequent to any step operation. the positioner
must be alloW!d to settle. This requires 20 mSec
total after the last step pulse is initiated. i.e.,
S mSec for the step motion and 15 mSec for
:>eUlmg.
NOTE: All of the foregoing operations can be overlapped,
if reQ'Jired.
Figure
6
shows the leJeva", timing diagram for a write oper·
ation. At t-II when the unit is ready, the WRITE ENABLE
interlace line goes true; this enables the Write Current
Source.
Since the trim erase gaps are behind the readlwrite gap,
TRIM ERASE control goes true 390IlSec after the WRITE
ENABLE interface line. It should be noted thill this value
is optimized between the requir!!fTlents at Track 130 and
Track
40
so that the effect of the trim erase gaps on pre·
vious information is minimized,
Figure 6 also shows the information on the WRITE DATA
interface Jine and the output of the Write Waveform Gen-
Cirator which toggles on the leading edge of every WRITE
DATA PlJlse.
Note thai a minimum 01 4 J-tSec and a maximum of 8pSec
betw~n WRITE ENABLE going true and the first WRITE
DATA pulse is only rl!(luireu if faithful reproduction of the
first WRITE DATA trilmition is significant.
At the end of recording, at
Il~ast
one addilional pulse on the
WR ITE DATA line must be inserted after the last significa....t
WR ITE DATA pulse to avoid exc:essive peak shift effects,
The TRIM ERASE signal must remain true for 800p$ec
after the termination of WRITE ENABLE to ensure that all
recorded data are trim erased. This value is again optimized
between the rKluirements at Tracks
I3li
and
40.
The duration of a write operation is from the true-going
edge of WRnE ENABLE
10
the falselloing
edge 01
TRIM
ERASE, This 1$ inuicalt!d by the i....ternal WRnE BUSY
w1l'lefnrm shown.
DATA REPRODUCTION
The Reat1 Elect rouics consists
01
lhe followi ....g:
.. Read Switch
.. ReM! Amplifier
.. Filter
.. D'fferenti<ttor
'It
Compilrator and Diyitiler
The Read SWitch is used
10
isolate the Read Amplifier from
electrical signals across the magnetic head during a write
operation.
Before reading can begin, the Drive must be in a ready con-
ditioo. As with the data recording operation, this ready
condition must
be
established by the user system, In addi-
tion to the requirements established in the paragraph,
DATA RECORDING, a 100 #Sec delay must exist from the
trailing edge of the TR 1M ERASE signal to allow the Read
Amplifier to scttle after the transient caused by the Read
Switch returning to the Read mode.
Referring to Figure 7, the output signal from the: read/write
head is amplified by a read amplifier and filtered to remove
noise by a linear phase Filter. The linear output from the
Filter is passed to the Dillerentiator which generates a
waveform whoS(! zero crossovers correspond to the peaks of
of the rcad signal. This signal is then fed to the Comparator
and Digitizer circuit.
The Comparator and Digitizer circuitry generates a 1 pSec
READ DATA pulse corresponding to each peak of the read
signal. This Composite Read Data signal is then sent to the
user system via the: READ DATA interface line.
99