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6.5.1
SC32A
Most
,
terminals, and printers require
the SC32A
lsolated RS232 lnterface
for
a "direct"
to the
21X. The
SC32A
raises the
21X's ring line when it receives
characters
frpm the computer or terminal, and
conveds the 21X's logic levels (0V logic low, 5V
logic high)
td RS232 logic levels.
The SC32A
P5
pin port
is
configured
as Data
Equipment (DCE)
which allows
to
Data
Terminal Equipment
SECTION
6.
9
PIN
SERIAL
INPUIIOUTPUT
Table 6.5-1 lists the most common RS232
configuration
for Data Terminal Equipment.
TABLE 6.5-1.
DTE
Pin
Configuration
PIN = 25-pin
connector number
ABR = Abbreviation for the
function name
O
= SignalOut
of
the
terminalto
another
device
|
=
Signal lnto the terminalfrom another device
PIN
2
ABR YO
FUNCTION
direct
(DrE),
includes
most PCs and printers.
For
to DCE devices such as
modems
some
computers, a null modem
cable
is reqqired.
When
the SC32A receives a character from the
computer or
terminal (pin 2), 5V is applied to the
datalogger
fling
line (pin
3)
for one second or
untilthe Mo{em
Enable line (ME)
goes
high.
The 21X wafts approximately 40 seconds to
receive
carrif,ge returns, which it uses to
establish
baird
rate.
After
the baud rate
is
set
the 21X tra4bmits
a
carriage return, line feed,
*,
and enters the
Telecommunications Command
State (Secti$n
5).
lf
the carriage returns are not
received within the
40 seconds, the 21X "hangs
up"
o
TD
Transmitted
Data:
Data
is
transmitted from the terminal
on
this line.
Received
Data:
Data
is
received by the terminal
on
this
line.
Request
to
Send: The
terminal raises this line to ask
a receiving device
if
the
terminal can transmit data.
Clear
to
Send: The
receiving
device raises this line to let
the
terminal know that the
receiving device is ready to
accept data.
Data
Terminal
Ready:
The
terminal raises this line to tell
the modem to connect itself
to the
telephone
line.
Data
Set
Ready:
The
modem raises
this line to tell
the
terminalthat the
modem
is connected to
the phone
line.
Data
Carrier
Detect: The
modem raises
this line to
tell the terminal that the
modem is receiving
a
valid
carrier signal from the
phone line.
Ring
Indicator: The modem
raises
this line to
tellthe
terminal that
the phone
is
ringing.
Signal
Ground:
Voltages are
measured relative to this
point.
NOTE: The SC32A
has
a
jumper.
With
the
jumper
{n
place
the SC32A blocks printer
data
an{
passes data only when the
21X
is
in
Telecbmmunications.
RD
RTS
O
CTS
I
DTR
O
DSR
I
DCD
I
6.5.2
COMPUTER/TERMINAL REQUIREMENTS
Computers,
terminals and printers are usually
configured
{s
Data
Terminal Equipment (DTE).
Pins
4
and 20
are used as handshake lines,
which
are set high when the serial port
is
enabled.
Pbwer for
the SC32A
is
taken from
these
pins.
For equipment configured
as DTE
a
direct
ribbortr
cable connects
the modem/terminal
to
the
SC3aA.
Clear
to Send (CTS) pin 5, Data
Set Ready {DSR) pin 6,
and Received Line
Signal Detept (RLSD) pin 8 are held high
by
the
SC32A (whbn
the RS232 section is powered)
which should
satisfy hardware handshake
requ
iremenfs
of
the modem/terminal.
22
SG
6-3
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