Tandy 1000
Joystick Interface
Technical Reference Manual
The joystick interface converts positional information from hand-held joysticks
(1
or
2)
into CPU data. Each joystick provides 1 or 2 push-buttons and
X,
Y
position for a total of 4 bits each. You can use 2 joysticks. The joystick handle
is
connected to two potentiometers mounted perpendicular to each other; one
for
X position, one for Y position. Through the cable, the main logic board ap-
plies
+ 5
VDC
to one side and ground to the other of the pots. The pot wiper
is
the position slgnal: a voltage between 0 and + 5 VDC. This signal
is
applied
to one input of a comparator U119.
The
other comparator input
is
the reference
signal
(a
ramp between 0.0 to + 5.0 volts.) When the position signal
is
equal
or less than the reference signal, the comparator output goes true. This com-
parator output
is
the X or Y position data bit. The ramp
is
reset to 0.0
VDC
whenever a
"write"
is
made
at
Port 200/201 Hex. The 10W* signal turns on
02,
which drains C6 to 0.0 volts. When
02
is
turned off,
01,
R3, R4,
R9,
and
CR1
create a constant-current source that linearly charges C6 to +5.0 VDC
in
1.12 milliseconds. The joystick information
is
"read"
by the CPU
at
Port
200/201 Hex through U18.
See
Figure
11.
Printer Interface
The
printer interface
is
totally contained
in
a custom Gate Array U108 and
is
shown
in
Figure 12. Functionally, the printer interface consists of
an
output
data latch (write
@ 378) and accompanying input data buffer. The latch and
buffer reads back the output data (read
@ 37
A)
with an accompanying input
buffer for read-back (read
@ 37
A).
The input buffer
is
for reading printer input
signals
(read@
379), I/O address decoding, data transceiver, and interrupt
logic. The interrupt
is
(logically) ACKNOWLEDGE *
if
interrupts are enabled
(37
A Bit
4).
34
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