Service manual
•
1526
AND
MPS
802
CIRCUIT
THEORY
+SV
1
kn
x 4
P5/P6
Serial
Interface
Connector
u;
a::
SQR
U2C
ATTN
3
2
r--t-------....,---=1
8
PAO
U2C
Clock
4
5
6
PSIP6
U2D
Pin
No.
Signal
10
p..:-;'-+.--=...oc
t-
____
....;1~3
PAS
U2D
1
SERIAL SRQ
8
r
9
____
---.:
'
....:..j4
PA6
2
GND
U2C
3
SERIAL ATN
Data
5
1--_---01---.:
1
:..;..1
d
~10=-----------':..::.j5
PA7
4
SERIAL
elK
5
SERIAL
DATA
RST
6
/-------0
6
RES
GND
2
Reset circuit
-=-
FG
TIMING
CHART
A~
____________
~
RECEIPT OF MESSAGE RECEIPT OF
DATA
PAS HIGH (PRINTER READY)
The
1526
and
MPS
802
Serial
Interface
Circuit
Theory
U4D
6532
The serial
interface
has bi-directional
DATA
and CLOCK signals. SQR (Service Request) is a hand-
shake
input
that
is
not
used.
ATTN
(Attention)
is a
"Iow"
active handshake signal. The printer ac-
cepts data on
the
DATA
input
(pin 5
of
P5
and P6)
after
the
ATTN
input
(pin 3
of
P5 and P6) goes
"Iow".
U2C pins 2 and 3 go
"high",
U2C pin 4 goes
II
low
II
,
U2D
pin
12
goes
"high",
and U2D
pin
10
goes
"Iow".
This is
the
DATA
output
which
acts as
an
acknowledgment
to
the
ATTN
input.
When
the
printer becomes ready
to
accept
data, U4D pin
13
(PA5) goes
"high",
U2D
pin 6 goes
"Iow",
U2D
pin
10
goes
"high".
ATTN
kept
"Iow"
by
the
transmitting
device indicates
commands
are being
transmitted
on
the
DATA
line. When ATTN is
"high",
data is being
transmitted
on the
DATA
line. Data is
input
on U2C pin
11.
The
output
of
the
inverter
U2C
pin
10
is
input
at
U4D
pin
15
(PA 7).
Data is clocked
into
the
printer
at
the
rate specified by
the
signal on
the
CLOCK
input
(pin 4
of
P5
and P6l._ The
Clock
signal is inverted by U2C, then
input
at
U4D
pin 9 (PA 1).
An
external reset
will
reset
the
processor logic inside
the
printer.
RESET
is on pin 6
of
P5 and P6.
17