11
UD70/MD29 Installation Guide
www.controltechniques.com
Issue Number: 3
3.3.3
Modbus ASCII
Mode 14 - 4 Wire Modbus ASCII Slave Mode
Mode 16 - 2 Wire Modbus ASCII Slave Mode
The UD70 and MD29 will communicate using the Modicon Modbus ASCII protocol
with a 4-wire or 2-wire connection. The data frame used for Modbus RTU is 1 start
bit, 7 data bits, no parity, 2 stop bits.
The following Modbus ASCII commands are supported:
FC3
PRESET SINGLE REGISTER
FC6
PRESET MULTIPLE REGISTERS
FC16
READ MULTIPLE REGISTERS
The maximum number of registers that can be transferred on a single message is
limited to 20, and the range of allowed node addresses is limited from 1 to 99.
3.3.4
Master/Slave
Mode 2 - Master Mode
Mode 3 - Slave Mode
In Mode 2, the node acts as a master, and continuously broadcasts a source
parameter, as defined by the Pointer parameter, from the RS485 port at a fixed
data rate of 9600 bits/sec. The value of the source parameter is scaled to ±16000.
In Mode 3, the node acts as a slave to receive the continuous data stream
transmitted by a Mode 2 master. The incoming data is multiplied by the scaling
parameter, and written to the destination parameter, as defined by the Pointer
parameter.
If the serial communications link is broken, the slave node can be made to trip. This
is done by setting the Global Trip Enable and RS485 Trip Enable parameters.
U n id riv e o r
M e n to r II
p a ra m e te rs
S c a le to + /-
1 6 0 0 0
P o in te r 1
S c a lin g
p ara m ete r
P o in te r 1
U n id riv e o r
M e n to r II
p a ra m e te rs
M a ste r N od e ( M o de 2)
S lav e N od e ( M o de 3)
R S 4 8 5 p o rt
3
7
1 6 2
R S 4 8 5 p o rt
3
7
1 6 2
