User`s guide
Vector
ZCB
Single
Board Ccmputer
It
is
not
within
the
scope
of
this
manual
to
detail
the
functioning
of
the
8251
USART
chip,
nor
to
teach
the
theory
of
serial
carmunication.
In
order
to
write
your
own
camnunications
software
or
to
rrodify
the
ZC8
serial
port,
you
will
need
to
be
thoroughly
familiar
with
this
<flip.
You
can
refer
to
Intel's
Application
Note
#16,
entitled
"Using
The
8251
Universal
Synchronous/Asynchronous
Receiver/rransmitter,"
which
Intel
will
provide.
This
Note
is
also
an
excellent
reference
on
basic
communications
theory.
More
readily
available
references
on
the
8251,
but
ones
that
have
less
to
say
about
o::mrm.mication
theory,
are
the
"INI'EL 8080
Microcomputer
Sys
terns
User's
Manual,"
available
either
fran
Intel
or
IJl()St
canputer
retail
stores,
and
Adam
Osborne's
"An
Introduction
to
Microcanputers,
Volu.rre
II
-
Sane
Real
Products,"
also
available
in
many
canpu.ter
stores.
1.5.2
serial
asynchronous
ccmnunication
You
can
select
the
rate
of
transmission
and
reception
fran
a
choice
of
110,
150, 300, 600, 1200, 2400, 4800,
or
9600
bits/second.
You
choose
the
rate
using
a
small
DIP-switch
on
the
toard.
If
you
are
writing
custan
software,
there
is
also
a
simple
way
to
divide
the
chosen
rate
of
a
port
by
4,
allowing
sane
software
control
of
the
rate
without
physically
opening
up
the
computer.
,
For
example,
if
you
have
a
modem
that
is
switch
selectable
for
either
1200
bits/second
or
300
bits/second,
you
can
write
a
prCXJram
that
enables
the
operator
using
the
keyboard
to
change
the
canputer'
s
rate
of
carmunication
to
match
that
of
the
m.:>dem
at
any
given
time.
You
can
select
via
software
the
number
of
data
bits
in
each
ASCII
character,
selecting
either
5,
6, 7,
or
8.
You
can
also
select
the
number
of
stop
bits
in
each
character,
selecting
either
1,
1-1/2,
or
2.
Finally,
you
can
select
whether
or
not
a
parity
bit
is
included
for
each
character,
and
if
chosen,
whether
or
not
it
is
even
or
rod
parity.
For
how
to
do
this
in
software,
see
the
references
given
earlier
for
the
8251
USARI'.
1.5.3
serial
synchronous
ccmnunication
You
can
enable
the
serial
port
to
carmunicate
in
the
synchronous rrode.
Modifications
to
the
board
will
be
required
to
accanplish
this.
In
brief,
the
8251
SYNDET
pin
and
the
TxC and
RxC
clock
pins
must
be
connected
to
the
outside
v.orld,
which
is
not
the
case
in
the
standard
configuration
of
the
toard.
Once
set
up
for
synchronous
oammunication,
you
can
select
the
rate
of
ccmnunication,
by
using
an
external
clock
between 0 and
56K
bits/second.
As
with
asynchronous
camnunication,
you
can
select
via
software
the
character
length,
selecting
either
5,
6,
7,
or
8
bits.
You
can
also
select
via
software
whether
or
not
a
parity
bit
is
included
for
each
character,
and
if
ch03en,
whether
or
not
it
is
even
or
odd
parity.
Also
via
software,
you
can
select
separately
for
each
port
whether
you
are
using
internal
or
external
synchronization,
and
whether
one
or
two synch
characters
are
used.
Rev.
1-8
6/11/80
1-3