SC105 CS I/O to RS-232 Interface
5
‘Modem mode’: DTR will be driven to +5 V when the CS I/O interface
is active for Modem Enable, SDC Address 9, and
Addressed Print Device configurations. When the
CS I/O is inactive, DTR will be 0 V.
Additionally, there will be a ‘dead time’ after DTR is
dropped of 2 seconds when data coming in on the RS-
232 will be ignored.
For SDC Address 7, 8, 10, or 11, DTR will always be
driven to +5 V.
RTS will ‘key’ the data; it will be driven (+5 V) 20 ms
prior to data being sent out the RS-232, and remain
driven for 5 seconds after the last data is sent out the
RS-232.
‘Custom mode’: This mode is identical to the ‘Modem mode’, except the
delays between RTS HI and data, data and RTS LO, and
the ‘dead time’ are all configurable.
4. Installation
Connect the SC105 to the RS-232 device and to the data logger with the SC12
9-pin cable. If the device has a 25-pin connector, a 9-pin female to 25-pin male
adapter is required.
Proper transient protection should be installed to protect the computer and data
logger in areas where damage due to lightning is possible. If this is a RAD
modem application, see Section
RAD Modem Wiring and Grounding
.
5. RAD Modem Application
The SC105 can be used with a short-range modem to communicate across a
4-wire, unconditioned dedicated line. Campbell Scientific offers a mounting
bracket that will mount the RAD, SC105, and adapter to the back plate in a
Campbell Scientific enclosure. This section describes using a short-range
asynchronous modem, SRM - 5A RAD modem.
For transmission, the RAD modem uses a cable made of two pairs of twisted
wires with a shield. Data rates up to 9600 bps are possible. The low voltage
transmission levels minimize cross talk between adjacent lines within the same
cable. Data are transmitted and received at a balanced impedance, providing
excellent immunity to circuit noise. TABLE
gives the data rate possible for
several gauge cables across several distances.
TABLE 5-1. Approximate Range, miles and km
Data Rate 19 Gauge (0.9 mm) 24 Gauge (0.5 mm) 26 Gauge (0.4 mm)
bps
miles
km
miles
km
miles
km
9,600
6.2
10.0
2.8
4.5
2.0
3.3
1,200
7.6
12.2
3.4
5.5
2.5
4.0
