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FUNCTION CO DE 16 – PR ES ET MULTIPLE REG ISTER FU NCT IO N CO DES
42 1TG C908004M0 201
8.8. Function Code 16 – Preset Multiple Register
Function code 16 performs the same function as FC06 but allows modifying the contents of
multiple output registers. That means it is possible to send the switching commands to several
M10x on a single write command.
The valid address range: 40001-49999
The MNS Digital Gateway will only send outgoing commands via FC 16 if there is a
change in value compared with the commands previously sent, thus decreasing bus
load. If this does not comply with users’ communication philosophy, FC 06 should
be used for commands so that each single command will be passed without
limitations.
When utilizing FC 16 it is good practice to, once the desired command has been
sent and successfully acted upon, then change the command code to NOP. This
will ensure that the M10x acts upon a ‘change of state’ from the command con-
trol
8.9. Restrictions
8.9.1. General
To ensure optimal performance, a maximum of 60 modbus requests per second is
allowed.
According Modbus standard MNS Digital Gateway supports up to 16 simultaneous
requests. Simultaneous means Modbus master don’t wait until response of MNS
Digital Gateway, DCS could send more new requests. Please keep in mind: DCS has
to count open requests and has to check that never more than 16 requests are
open.
8.9.2.
Modbus RTU
MNS Digital Gateway with Modbus RTU in redundant configuration does not reply
to Modbus requests (except FC08) if switchgear bus is not connected properly.
Thus the DCS can easily detect a communication problem and use the redundant
communication line.
The response time of a modbus slave depends on several parameters, for instance
baudrate, number of registers in request and/or reply. Due to this the following
procedure for DCS is recommended:
1. DCS sends modbus requests
2. DCS receives modbus reply from slave
3. After receiving of complete modbus reply DCS waits 100ms (or more if from
DCS application required)
4. DCS sends next modbus request