User`s guide
Vector
ZCB
Single
Board COmputer
from
the
original
purpose
for
RS-232C -
to
connect
a
terminal
with
a
communication
device
such
as
a modem. A
computer
does
not
have
to
be
involved
at
all.
Since
a
canputer
can
either
play
the
part
of
a
terminal,
when
connected
to
a modem,
or
it
can
play
the
part
of
communication
equiprent,
when
connected
to
a
tenninal,
accmputer
serial
tx>rt
can
be
used
either
as
LeE
or
DI'E. However, a
given
serial
{X>rt
can
only
be
wired
up as
one
or
the
other
at
anyone
time.
If
the
port
happens
to
be
wired
up
to
look
like
OCE,
and
you
want
to
connect
it
to
another
OCE
such
as a
Irodem,
then
the
RS-232C
connection
will
not
'WOrk.
Both
ends
'WOUld
be
transmi
tting
on
the
same
lines
and
receiving
on
the
same
lines.
Before
the
RS-232C
connection
can
be
made,
in
this
case,
you must
rewire
the
canputer'
s
ser
ial
tx>rt
so
that
it
receives
and
transmits
on
the
lines
specified
for
DI'E.
1.5.5
RS-232C
on
the
ZCB
To
enable
the
serial
tx>rt
to
communicate
over
an
RS-232C
line,
you
will
connect
one
end
of
this
line
to
the
serial
tx>rt
socket
on
the
ZCB
roard,
and
the
other
end,
having
an
RS-232C
standard
DB-25
femal~
connector,
to
the
back
panel
of
the
computer.
The
cable
is
designed
so
that
appropriate
signals
fran
the
board
are
directed
to
the
RS-232C
lines
at
the
DB-25
connector
as
if
it
were
Data
Camnunications
Equipment.
Thus,
the
resulting
DB-25
socket
at
the
rear
of
the
ccmputer
is
a
OCE
RS-232C tx>rt.
Drivers
are
provided
for
the
serial
port
to
enable
the
8251
Transmit
Data
and
Receive
Data
lines
to
input
or
output
at
RS-232C
voltage
levels.
These
receivers
and
drivers
are
already
connected
on
the
board,
requiring
no
jurnpering.
When
a
serial
I/O
cable
is
installed
these
signals
are
connected
to
RS-232C
lines
3
and
2
respectively.
In
addition,
four
of
the
RS-232C
control
lines
are
connected
to
the
appropriate
pins
on
the
8251.
These
are
1Jl'R,
OOR,
RI'S
and
Cl'S.
See
the
table
"Additional
RS-
232C
handshaking
lines
available"
in
Section
2.
4.
2
for
the
pin
assignments.
When
a
serial
I/O
cable
is
installed,
these
signals
are
available
on
the
cable's
DB-25.
There
are
four
other
signals
available
fran
the
8251
whidl
can
be
accessed:
TxRDY,
TxMl',
SYNDET
and
RxRDY.
You
can
install
jumpers
and
RS-232C
line
drivers
to
enable
the
8251
to
dynamically
control
any
two
of
them
via
software.
Further,
a number
of
other
RS-232C
lines
are
available
on
the
board
using
the
standard
serial
I/O
cable
mentioned
above.
These
are
both
input
and
output
lines,
but
they
are
not
connected
to
anything
other
than
pads
on
the
board,
nor
are
drivers
and
receivers
connected
to
them. The
table
"RS-232C
and
Connections
on
ZCB
Board"
in
Section
2.4.6
lists
the
functions
of
each
of
these
lines.
Any RS-232C
line
can be
connected
to
+12
VOC
on
the
roard.
In
addition,
for
eadl
tx>rt,
the
8251
can
be
used
to
nonitor
in
software
anyone
RS-232C
handshaking
line,
and
the
8251
can
be
used
to
control
fran
software
the
output
of
any
two
RS-232C
handshaking
lines,
and
lastly,
the
825l's
transmitter
can
be
disabled
or
enabled
by
anyone
RS-232C
incoming
Rev.
l-B
6/11/80
1-5