Campbell Scientific MD9 Coax Multidrop Interface - Manual (Page 5)

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MD9 Multidrop Interface
1. Introduction
The MD9 Multidrop Interface functions as a direct wire link between a
computer and a Campbell Scientific datalogger via coax cable. MD9s may be
networked thereby permitting a computer to address and communicate with up
to 254 dataloggers. Total coax length may be up to 3 miles when fewer
dataloggers are used.
With the communication link initiated and controlled by an IBM PC or clone
using Campbell Scientific's telecommunication software, the operation of the
MD9 in the system is transparent to the user. Call back from a remote
datalogger via MD9 is not possible.
TABLE 1-1. Specifications
Size: 6.5 X 3.5 X 1.25 in.
Weight : 5 oz.
Accessories: SC12 cable, BNC "T" connector
Voltage: 5 Volts from datalogger or SC532(A)
Current:
State 0 "Standby" 1.2 mA
State 1 "Active" 17 mA
(when transmit line drives network) 80 mA
State 2 "Sleep" 3 mA
State 3 Pull ring line & buffer bytes 17 mA
Temperature range: -25 to +50 o C
Baud rates: 9600, 1200, 300
Carrier frequency: 1.2 MHz
Communication cable: RG59/U Coax
Cable connector: BNC
2. System Description
The block diagram in Figure 2-1 depicts the connection of a computer to a
network of Campbell Scientific dataloggers using MD9s.
Connection of the MD9 to the computer's RS-232 SIO port is made via the
SC532(A) 9 Pin Peripheral to RS-232 Interface. The SC532(A) supplies +5
VDC power to the MD9 as well as converts the MD9's CMOS voltage levels to
voltage levels consistent with RS-232 requirements. A computer with the
PC201 card installed could use the SC925 Cable to connect directly to the
MD9.