Setra System Model 370 - Manual (Page 39)

III.7 RS-232 INTERFACE HARDWARE
The RS-232 Communication Standard describes in detail the requirements
and conventions of RS-232. For most applications, the information given here
is sufficient to solve any problems.
The Setra Digital Pressure Gauge implements the majority of the RS-232
communications standards, but does not provide handshaking lines (such as
busy, DSR, or DTR).
The four lines which must be connected are diagrammed below, along with
the pin layout of the female connector on the back of the gauge.
13 7 3 2 1 PIN DESC.
O O O O O O O O O O O O O 1 Protective ground
O O O O O O O O O O O O 2 Input to gauge (RXD)
25 14 3 Output from gauge (TXD)
7 Signal ground
The Model 370 serial interface is a DCE (Data Communications Equipment)
type, with a standard female DB25S pin connector. This means that it receives
data on pin 2 and sends data on pin 3. This is in contrast to DTE (Data Trans
mission Equipment) which receives data on pin 3 and sends data on pin 2. The
RS-232 standard describes communications between DTE and DCE devices.
Since many computers have serial ports configured as DTE, the Model 370
conveniently plugs directly into the standard serial port on most computers,
using a standard RS-232 "straight-through" cable available from SETRA, or
from any computer hardware vendor.
Some devices, including some printers and computers, will be equipped
with DCE interfaces like that in the Model 370. To connect the Model 370 to
these devices, a "null modem" cable is required. This is simply a cable which
connects pin 2 and 3 of the Model 370 to pin 3 and 2 of the other device
respectively by crossing them in the cable. This kind of cable is also available
from SETRA, or from any computer hardware vendor.
The maximum recommended cable length is 15 meters.
The RS-232 data format used by the Model 370 is :
8 bits
1 start bit
1 stop bit
no parity.
For more information, consult RS Standard RS-232, or contact a SETRA
Applications Engineer.
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