Tandy 1000 Technical Reference Manual

Tandy 1000
Technical Reference Manual
Outputs of the direction latch and the internal step pulse generator
are input to the shift register and phase drive selector, and they
are converted to the appropriate timing signals for uni-polar 1-2
phase drive of the 4-phase stepping motor. These phase drive signals
are supplied to the stepping motor driver, US (output pins 12 ~ 15).
In order to improve the torque margin in the seek operation, partially
2-phase drive period is provided by the phase drive selector only in
the initial stage when the drive phase is changed.
When the head stops on an even track, phase A is magnetized, while
phase A is magnetized when the head stops on an odd track. The phase
Band B are magnetized only during the seek operation.
The output from the internal step pulse generator is also supplied to
the over-drive timer constructed with a re-triggerable counter.
During the active period of this timer (7Smsec, approx.), +12V power
is supplied to the stepping motor coils through the over-drive circuit
(Ql) to produce enough torque required for the head seek and the
settling operations. After the completion of the settling, only +SV
power is supplied to the stepping motor through the diode, CRl, which
minimize the power loss by supplying only the required torque for the
holding of the stop position. By the above consideration, heat
radiation from the motor is depressed to the minimum level and the
stepping motor power consumption of O.33W, approx. at the stop
condition is achieved.
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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