GE Industrial Solutions GE ZENITH SERIES MDU - Manual (Page 31)

System Monitoring
GE Z ENITH C ONTROLS
MDU Owner’s Manual
601 S HILOH R OAD January 2013
Plano, TX 75074 Page 31
c. Registers
Most of the analog values are 2 byte integers representing a parameter such as input
voltage, current, etc. KWH takes 2 of the 2-byte integers. Some parameters require
scaling, and are noted in the points list.
d. Prerequisites
Each connected monitor must have a unique address between 1 and 255. The Setup
screen is used to set up the address of the monitor. It also uses additional sequential
address for each device. The number of devices is also in the setup screen.
Note: improper configuration of a GE Zenith Series Monitor may block other
monitors or devices on the chain.
e. Biasing and Termination
Since there is only one master, the master can and should drive its transmit pair
continuously. But slaves do not drive the master’s receive pair until they send the
master a response. As soon as they are finished, they stop driving the master’s receive
pair. This is necessary since other slaves may need to send responses on the master’s
receive pair. Therefore, most of the time the master’s receive pair is just floating. The
master’s adapter SHOULD drive its transmit pair continuously and, of course, never
drive the receive line, except in an effort to be 2 wire compatible. Most adapters do not
drive the transmit pair until the start of the first character sent, and only continue to
drive the transmit pair a few milliseconds after the last character (meaning the
master’s transmit pair is usually just floating most of the time).
f. Wiring
RS485/RS422 cable length can be up to 4000ft if the proper cable is used. To achieve
this you need to have a shielded cable with 2 twisted pairs and shield/ground. The two
transmit lines need to be in one twisted pair and the two receive lines need to be in the
other twisted pair. The cable resistance should be 27 ohms/1000ft @ 1 kHz or less and
the mutual capacitance should be 14pf/ft @ 1 kHz or less. RS422 is typically (4) four
wire, and RS485 is typically (2) two wire and is slower than RS422.
g. Supported Commands and Replies
Note that these are typical for the product. See the point list for specifics .
a. Report slave ID
Sent Hex: 01 11 C0 2C
Reply Hex: 01 11 0D EA FE 52 50 50 20 44 69 73 70 6C 61 79 A3 A6
b. Read holding registers
Sent Hex: 01 03 00 00 00 01 84 0A
Reply Hex: 01 03 02 00 00 B8 44
c. Write single register
Sent Hex: 01 06 00 00 00 00 89 CA
Reply Hex: 01 06 00 00 00 00 89 CA
The flag and data numbers shown here are in “human” numbers. The first analog
channel is numbered 1 but, in software, it is accessed by an index value of 0. It is
common for a system to be one register off due to this situation, so it is important to
verify that the registers are correct early in the configuration procedure. As similar
readings are in adjacent registers, being one register off is not necessarily apparent.