PacComm TINY-2 - Page 132

HARDWARE
DESCRIPTION
Modem
Disconnect
-
JS.
+
Power
Supply:
The
7805
regulator
(U5)
supplies
the
main
portion
of
the
board
with
clean,
stable
5
volt
power.
The
incoming
positive
voltage
is
routed
through
a
choke
(L1)
and
diode
(D6)
for
reverse
polarity
protection
and
to
the
power
switch.
It_
feeds
the
7805
regulator
and
pin
14
of
the
MAX
231
IC
(U15),
The
MAX
231
has
internal
oscillators
which
allow
it
to
generate
a
negative
voltage
to
support
the
RS232
levels.
A
voltage
approximately
one
volt
below
the
incoming
supply
voltage
can
normally
be
measured.
The
battery
circuit
is
isolated
by
diodes
to
keep
the
RAM
and
the
74HC132
powered
whenever
JP-B
is
installed.
The
TINY-2
requires
approximately
220
ma
at
9-14
vde
[MICROPOWER-2
=
40
ma.]
Modem Disconnect - J5
The
modem
disconnect
on
the
TINY-2/MICRO-2
PC
board
(J5)
Is
provided
for
using
higher-speed
modems,
or
more
sophisticated,
higher-performance
modems
for
satellite
or
other
uses.
This
connector
is
the
same
as
the
TAPR
TNC-2
header.
Aphysical
connector
for
J5
is
installed
on
the
MICROPOWER-2,
but
not
on
all
versions
of
the
TINY-2.
Any
standard
20-pin
header
for
use
with
IDC
cable
connectors
should
be
suitable
for
installation
on
the
TINY-2,
Parts
are
available
from
PacComm.
When
installing
the
con-
nector,
be
sure
to
line
up
the
marked
pin
(pin
1
)
of
the
header
with
the
the PC board
pin 1 marking.
To
use
an
external
modem,
it
is
necessary
to
cut
the
traces
between
pins
1-2
and
17-18
on
the
bottom
of
the
TINY-2/MICRO-2
PC
board
with
a
sharp
knife
or
MotoTool.
If
RX
Clock
is
provided
by
the
external
modem,
then cut 13-14.
If CTS is provided,
cut 9-10.
[QAUTION:
DO
NOT
GUT
ANY
OTHER
TRACES
WHICH
MAY]
yPASS THROUGH THE J5 AREA AND WHICH ARE NOT}
[CONNECTED
TO
J5
PINS!
_!
Once
the
traces
are
cut
at
J5,
you
must
install
push-on
jumpers
or
a
shorting
connector
on
the
above
pin
pairs
to
use
the
on-board
modem.
This also applies to the MICROPOWER-2.
The
signals
used
at
connector
J5
are
at
standard
TTL
interface
levels.
ATIL
high
is
greater
than +2.4
volts
but
fess
than
+5.25
volts.
ATTL
low
is
Jess
than
0.4
volts
but
greater
than
0
volts.
If
you
elect
to
use
an
off-board
modem,
be
sure
to
properly
shield
the
interconnecting
cables
for RFI protection.
J5 Pin Definitions
The
following
information
is
primarily
for
those
who
wish
to
interface
external
modems
to
the
packet
controller.
Familiarity
with
modem
and
serial
data
channel
terms
is
assumed.
TINY-2/MICRO-2
Technical
Ref.,
2
Ed
©
1989,
PacComm,
Inc.
1