11
4.3.1 RS-422 Connection
It is recommended that screened 2 x twisted pair cable is used for RS-422 con-
nection in order to minimize signal errors due to noise. An option fifth wire, con-
necting the common (0v) at each unit, is recommended for optimum performance.
The first pair should be used for RXA and RXB and the second for TXA and TXB.
The screen should be connected to the connector housing (ground) at the host
only. To reduce cable reflections over long distances, RS-422 systems require line
termination. This is achieved by fitting two 120
⍀
terminating resistors as shown in
figure 4.5. One resistor should be fitted at the Host receive input buffer and the
other at the receive buffer of the most remote meter.
Figure 4.5. RS-422 Multi-Drop Connection
22
4.5.7 Table 16 Current and Voltage Demand
Notes:
5. Use “Amps Scale” at Addr 2837 to convert to real Amp Demand.
6. Use “Ph Volts Scale” at Addr 2838 to convert to real Volts Demand.
The rolling demand averages of currents and voltages are available in Table 16 as
unsigned integers.
Note:
Tables 15 and 16 are only available in GIMA meters with software ver-
sions 1.04 or later. An invalid table exception will be returned on earlier
meters.
4.5.8 Function 04 (or 03) Read Multiple Registers
Description
This function allows a number of registers from a meter table to be read in a single
operation. This command is commonly used to obtain instantaneous, energy or
set-up data from the meter. This command is not available as a broadcast com-
mand, as it requires a return data packet from the meter
Host Request
The example above shows a read of three consecutive Integers from the Instanta-
neous Data Table 11 (OBH), offset 0. The meter accessed has a Modbus ID of 25
(19H).
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