Campbell Scientific CR7 Measurement and Control System - Manual (Page 65)

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 CR7. The
SC32A raises the CR7's ring line when it
receives characters from the computer or
terminal, and converts the CR7'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, use
SC932 interface in place of SC32A.
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 CR7 waits approximately 40 seconds to
receive carriage returns, which it uses to
establish baud rate. After the baud rate is set
the CR7 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 CR7 "hangs
up".
NOTE: The SC32A has a jumper. With the
jumper in place, the SC32A blocks printer
data and passes data only when the CR7 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.