Operator`s manual

SECTION 6. 9 PIN SERIAL INPUT/OUTPUT
6-3
6.5.1 SC32A INTERFACE
Most computers, terminals, and printers require
the SC32A Optically Isolated RS232 Interface
for a "direct" connection to the 21X. The SC32A
raises the 21X's ring line when it receives
characters from the computer or terminal, and
converts the 21X's logic levels (0V logic low, 5V
logic high) to RS232 logic levels.
The SC32A 25 pin port is configured as Data
Communications Equipment (DCE) which allows
direct connection to Data Terminal Equipment
(DTE), which includes most PCs and printers.
For connection to DCE devices such as
modems and some computers, a null modem
cable is required.
When the SC32A receives a character from the
computer or terminal (pin 2), 5V is applied to the
datalogger Ring line (pin 3) for one second or
until the Modem Enable line (ME) goes high.
The 21X waits approximately 40 seconds to
receive carriage returns, which it uses to
establish baud rate. After the baud rate is set
the 21X transmits a carriage return, line feed, *,
and enters the Telecommunications Command
State (Section 5). If the carriage returns are not
received within the 40 seconds, the 21X "hangs
up".
NOTE: The SC32A has a jumper. With the
jumper in place the SC32A blocks printer
data and passes data only when the 21X is
in Telecommunications.
6.5.2 COMPUTER/TERMINAL REQUIREMENTS
Computers, terminals and printers are usually
configured as Data Terminal Equipment (DTE).
Pins 4 and 20 are used as handshake lines,
which are set high when the serial port is
enabled. Power for the SC32A is taken from
these pins. For equipment configured as DTE a
direct ribbon cable connects the modem/terminal
to the SC32A. Clear to Send (CTS) pin 5, Data
Set Ready (DSR) pin 6, and Received Line
Signal Detect (RLSD) pin 8 are held high by the
SC32A (when the RS232 section is powered)
which should satisfy hardware handshake
requirements of the modem/terminal.
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 = Signal Out of the terminal to another
device
I = Signal Into the terminal from another device
PIN ABR I/O FUNCTION
2 TD O Transmitted Data: Data is
transmitted from the terminal
on this line.
3 RD I Received Data: Data is
received by the terminal on
this line.
4 RTS O Request to Send: The
terminal raises this line to ask
a receiving device if the
terminal can transmit data.
5 CTS I Clear to Send: The receiving
device raises this line to let
the terminal know that the
receiving device is ready to
accept data.
20 DTR O Data Terminal Ready: The
terminal raises this line to tell
the modem to connect itself
to the telephone line.
6 DSR I Data Set Ready: The
modem raises this line to tell
the terminal that the modem
is connected to the phone
line.
8 DCD I 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.
22 RI I Ring Indicator: The modem
raises this line to tell the
terminal that the phone is
ringing.
7 SG Signal Ground: Voltages are
measured relative to this
point.