Tandy 1000 Technical Reference Manual

Tandy 1000
(2) Write circuit
Technical Reference Manual
The write circuit consists of write power gate (with side selector),
select gate, data latch, write driver, and erase driver.
The write power gate output (COMO or COM1) becomes high voltage when
the write gate signal or the erase gate signal is TRUE (HIGH level).
These signals are generated by the write/erase gate in the control
circuit when all of the following three conditions are satisfied.
(a) The file protect sensor detects the notch of the disk jacket (write
enable condition).
(b) The WRITE GATE input signal is TRUE.
(c) MX strap is on or the DRIVE SELECT signal is TRUE (LOW).
The write power gate output is supplied to the common terminal of the
head through the diode switch. Table 301 shows the output voltage of
the write power gate in various operations.
Conditions
Write power
gate output voltage
COM 0
(for Side
0)
COM 1 (for Side
1)
Side
0
write
operation
High
Low
Side
1 write
operation
Low
High
Side 0
read operation
Middle
Low
Side 1
read
operation
Low
Middle
High: 10.5V, approx.
Middle: 4V, approx.
Low: OV, approx.
(Table 301) Write power gate output voltage
For the tunnel erase head, the erase gate signal is delayed appropriate-
ly against the write gate signal. Since the erase gap is about 0.85mm
behind the read/write gap, it is necessary for the erase driver to
delay the write gate signal so that the written data is completely
trimmed by the erase head (tunnel erase).
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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200