User`s guide
vector
ZCB
Single
Board Ccmputer
anything.
Software
can
tell
that
the
8251
is
ready
to
transmit
by
monitoring
the
TxRDY
bit
in
the
status
byte,
or
by
being
interrupted
by
the
TxRDY
8251
output
(pin
15).
For
infotmation
on
the
8251
status
byte,
refer
to
one
of
the
8251
references
rrentioned
in
the
Perspective
section
of
this.
manual.
Remember
that
if
you
are
connecting
a
serial
port
to
a
rrOOE!m
or
other
Da.ta
Ccmnunications
EXJUiprent,
BOO
you
are
not
usirg
the
Null
Modem
Cable,
you
should
disconnect
RS-232C
lines
5 and 6
fran
the
+12
VOC
source
on
the
board,
unless
you
are
p:sitive
it
p:ses
no
danger
to
the
Da.ta Ccrrmunications
EXJUipnent.
If
you
ARE
using
a
Null
Mc:xlem
Cable,
the
+12
VDC
signals
are
routed
to
RS-
23
2C
lines
4,
2
0,
and
19
respectively,
on
which
the
Da.ta
Camlunications
Equiprent
CAN
receive
+12
VOC
without
harm.
Therefore,
when
using
a
Null
Modem
Cable,
you
do
not
have
to
disconnect
a
line
fran
+12
VOC
unless
you
want
to
control
the
status
of
that
line
fran
software.
To
control
an
RS-232C handshaking
line
fran
software,
it
must
pass
fran
an
8251
output
pin
to
the
input
of
one
of
the
driver
circuits
in
a 1488
quad
line
driver.
It
must
then
pass
fran
the
output
of
this
1488
driver
circuit
to
the
RS-232C
line.)
TO
respond
to
an
incoming RS-232C
handshaking
line,
it
must
pass
to
the
input
of
one
of
the
receiver
circuits
in
a 1489 quad
line
receiver.
It
must
then
pass
fran
the
output
of
this
1489
receiver
circuit
to
one
of
the
8251
input
pins.
For
reference:
1488 = a quad
line
driver.
1489 = a quad
line
receiver.
There
is
one
spare
receiver
circuit
and one
spare
driver
circuit
on
the
board.
'!be RS-232C
input
to
the
spare
receiver
is
U16
pin
13
and
its
output
is
U16
pin
11.
The
input
to
the
spare
driver
is
U15
pin
2
and
its
RS-232C
output
is
U22
pin
3.
Wire
your
jumpers
directly
to
these
pins,
when
required.
2.4.7
Using
the
parallel
p:?rts
As
shown
in
the
introductory
I/O
section,
Parallel
FDrt A
is
I/O
address
x8
(usually
08),
Parallel
Port
B
is
I/O
address
x9
(usually
09),
Parallel
Port
C
is
xA,
(usually
OA)
and
the
address
of
the
Control
Status
Register
is
xB
(usually
OB).
'!bese
ports
can be used
as
is,
without
jumpering.
You
can
interface
to
the
34-pin
connector
J1
at
the
tcp
of
the
board
using
the
ZCB
Parallel
I/O
cable
supplied
by
Vector
Graphic.
This
cable
comes
with
no
connector
at
the
far
end,
enabling
custanization.
2-18
Rev.
I-B
6/11/80