Radio Shack TRS-80 Service Manual page 34
Pocket computer printer and cassette interface
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Also See for TRS-80:
- Reference manual (274 pages) ,
- User manual (236 pages) ,
- Service manual (199 pages)
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Rcfcring to
the
block
diagram,
the 26·3605
is
the printer (DGP1301) and the CMT
(casselle tape
record°' interface) which
consists of
three
blocks,
the CMT
interface,
printer
interface
an.d power
supply circuit.
•
CMT
interfa~
The
CMT
int
erface
is
the
c ircuit
tha1
handles
dala transfer
be1ween
the
l'C·2 and
the CMT
and
consists
of a simple
d
river
circuit
(voltage
le
... el
conversion
circuit).
In
addition,
there is the
CMT
on/off
remore controUing
circuit
which i.< under the
program cont
rol of
the
PC-2 and
perfomlS
switching
operation
via the 1/0
port
using
the
relay ci.rcuit.
•
Printer interface
·n1e printer inrerface
consisrs
or
character generator
ROM
(LHS367-02),
1
/0 porr
(LH5801),
motor
drive
circuit,
prim
solenoid
drive
circuit,
and the pen color detect input signal circuit
.
•
Power
supplv
block
A simple
power
stabilization circuit
is
pro\•ided
to
take
care
of
recharging to
the built-in NiCd
batteries
from the
J\C
adaptoc.
(Refer
the
section of
circuit
diagram
for
adjusti.ng)
3. CIRCUIT DESCRIPTION
3-1. CMT
Interface circuit
d
iagram
Cf.
150
PC-2
18Kn
0.0047,;·
tOKn
O.t,
V
,.......,w--.,~IJ--Ml'--..--f
II-..----{(~
M
IC
Z?Oil
270ll
CMTOUT
110
port
I Mil
TC40JIOOOP
·111e
signal CMT
OUT
is
sent from
the
PC-2 to wrice data
011
the cassette tape and the
capacitor
coupled
interface circuit is
provided to
stufl
the
voltage level before
supplying
t
he
MIC
jack
.
T he read signal
is
the
input
from rhe EARPHONE
jack
and
passed
th
rough
the
capacitor and
two
stages
of
gates to perform
voltage
level shifr
and
waveform shaping
and
delivered to rhc
Pc.2
as the
CMT IN
signal.
With
respect
to the CMT IN
signal,
the gate
input to
the
firs•
stage of
the gate
is
forced to a
low
level
by means of
the
PAO
signal
as
there is
a possibility
o
f supplying noise to
the EARPHONE jack as
input
dat
a to
the
PC-2
,
excep1 during the
data
read
mode.
•
Recording
signal
When
the
co
nrents
of the
srarr
bit o
r
data
bit
is
"O", four.
pulses of
l.27kHz are
recorded
in
a
t
ime of 3
.
I
Sms. When
the
contents of the data bit
is"!",
eight
pulses
or
2.S4kHz
are recorded in
the tape in a time
of3.J
Sms.
Shown below
is
an example
of the
contents
of
S (one
byre)
is"~
.
¥"·
Do not sale this PDF !!!
-30-
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