Radio Shack TRS-80 III User Manual

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 Generator, Erase Current Source, and Trim Erase
Control Logic.
The read/write winding on the magnetic head is center-
tapped. During a write operation, current from the 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:
(1) Drive speed stabilization. This condition will
exist 250 mSec after starting the drive motor.
(2) Subsequent to any step operation, the positioner
must be allowed to settle. This requires 20 mSec
total after the last step pulse is initiated, i.e.,
5 mSec for the step motion and 15 mSec for
settl ing.
NOTE: All of the foregoing operations can be overlapped,
if required.
Figure 6 shows the relevant timing diagram for a write oper-
ation. At t = 0 when the unit is ready, the WR ITE ENABLE
interface line goes true; this enables the Write Current
Source.
Since the trim erase gaps are behind the read/write gap,
TRIM ERASE control goes true 390pSec after theWRITE
ENABLE interface line. It should be noted that this value
is optimized between the requirements at Track 00 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 line and the output of the Write Waveform Gen-
erator which toggles on the leading edge of every WRITE
DATA pulse.
Note that a minimum of 4 pSec and a maximum of 8 pSec
between WR ITE ENAB LE going true and the first WR ITE
DATA pulse is only required if faithful reproduction of the
first WR ITE DATA transition is significant.
At
the end of recording, at least one additional pulse on the
WR ITE DATA line must be inserted after the last significant
WR ITE DATA pulse to avoid excessive peak shift effects.
The TRIM ERASE signal must remain true for 800pSec
after the termination of WRITE ENABLE to ensure that all
recorded data are trim erased. This value is again optimized
between the requirements at Tracks 00 and 40.
The duration of a write operation is from the true-going
edge of WRITE ENABLE to the false-going edge of TRIM
ERASE. This is indicated by the internal WRITE BUSY
waveform shown.
DATA REPRODUCTION
The Read Electronics consists of the following:
* Read Switch
* Read Amplifier
* Filter
* Differentiator
* Comparator and Digitizer
The Read Switch is used to 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-
dition. 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 pSec delay must exist from the
trailing edge of the TR 1M ERASE signal to allow the Read
Amplifier to settle 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 Differentiator which generates a
waveform whose zero crossovers correspond to the peaks of
of
the read 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

Radio Shack TRS-80 III Specifications

General

Brand	Radio Shack
Model	TRS-80 III
Category	Desktop
Language	English