PacComm TINY-2 - Page 127

COMPUTER
INTERFACING
RS-232C
Handshaking
Protocol
RS-232C
Handshaking
Protocol
6
The
CTS
and
ATS
lines
of
the
TINY-2/MICRO-2
serial
port
(labeled
P4
on
the
circuit
board
and
RS-232C
on
the
rear
panel)
are
used
by
the
TINY-2/MICRO-2
firmware
for
hardware
“handshaking”
to
control
the
flow
of
data
between
the
computer
and
the
packet
controller.
The
TINY-2/MICRO-2
always
asserts
(makes
true)
Data
Set
Ready
(DSR)
on
P4
pin
6
via
a
pullup
resistor.
Thus,
whenever
the
TINY-
2/MICGRO-2
is
powered
up,
it
signals
to
the
computer
connected
to
P4
that
the
packet
controller
is
“on
line.”
The
computer
terminal
indicates
it
is
ready
to
receive
data
from
the
TINY-2/MICRO-2
by
asserting
its
Request
To
Send
(RTS)
signal
on
P4
pin
4.
The
packet
controller
will
send
data
when
RTS
is
asserted
(if
there
is
data
to
be
sent).
If
the
computer
is
not
ready
to
receive
data,
it
negates
(make
false)
RTS
to
the
TINY-2/MICRO-2.
Thus,
data
flow
from
tne
packet
controller
to
the
computer
is
controlled
by
the
use
of
the
RTS
line.
The
packet
controller
asserts
its
Clear
To
Send
(CTS)
output,
P4
pin
5,
whenever
it
is
ready
to
receive
data
from
the
computer.
If
the
TINY-2/MICRO-2's
buffers
fill,
it
will
negate
CTS,
signaling
the
com-
puter
to
stop
sending
data.
The
packet
controller
will
assert
CTS
when
it
is
again
ready
to
receive
data
from
the
computer.
Thus,
data
flow
from
the
computer
to
the
packet
controller
is
regulated
by
the
use
of
the
CTS
line.
The
CTS
line
is
always
toggled,
even
if
“software
flow
control”
is
enabled
in
this
direction.
If
“software
flow
control"
is
preferred,
or
if
the
computer
terminal
serial
¥O
port
does
not
implement
CTS/RTS
and
DTR/DSR
handshaking,
then
a
three
wire
cable
should
be
used.
if
these
RS-232
control
lines
are
not
connected
they
will
be
pulled
up
(and
thus
asserted)
by
resistors
at
the
TINY-2/MICRO-2
end
and
proper
operation
will
result.
However,
a
non-standard
serial
port
may
use
some
pins
for
other
purposes,
such
as
supplying
power
to
a
peripheral
device,
so
be
sure
that
the
system
either
implements
the
CTS,
RTS
and
DSR
handshake
or
has
no
connections
to
these
pins
of
P4
whatsoever.
Note
that
reference
to
RS-232C
“compatibility”
or
the
presence
of
a
DB-25
type
connector
does
not
guarantee
that
you
have
a
standard
RS-232C
serial
port!
The
PacComm
TINY-2/MICRO-2
packet
controller
supports
asynchronous
computer
terminal
baud
rates
of
300,
1200,
2400,
4800
and
9600
and
19,200.
The
port
supports
standard
parity
options
as
well
as
7-
or
8-bit
character
lengths.
Factory
settings
are
1200
bauds,
eight
bit
wordlength,
no
parity
and
one
stop
bit.
(UK
=
1200,7,E,1)
if
you
want
to
interface
the
TINY-2/MICRO-2
with
a
device
configured
as
DCE,
such
as
a
telephone
modem
or
another
packet
controiler,
a
so-called
"nul!
modem"
cable
may
be
constructed
to
interchange
the
data
and
handshake
signais.
TINY-2/MICRO-2
Technical
Ref.,
2
Ed
©
1989,
PacComm,
Inc.