DUEMMEGI
MCP 4 – User's manual
Contatto
V19
=
I1.3
V20
=
I1.4
V21
=
I1.5
V22
=
I1.6
V23
=
I1.7
V24
=
I1.8
O1.1
=
V1
// Copy the received virtual points to the outputs
O1.2
=
V2
O1.3
=
V3
O1.4
=
V4
O1.5
=
V5
O1.6
=
V6
O1.7
=
V7
O1.8
=
V8
R1
=
AI2
// Copy the analog input to second register
AO2
=
R0
// Copy the first register to analog output
In practice, the status of inputs
I1.1
..
I1.8
of the module connected to the 1
st
MCP 4 will be copied to
V1
..
V8
of the same MCP 4 and published on the networks. The 2
nd
MCP 4 receives the status of these
virtual points and it stores them in the same position
V1
..
V8
, thus transferring the status to output module
O1
connected on its bus. The same thing happens in the reverse way through the virtual points
V17
..
V24
;
the same mechanism also applies to the registers.
2.1.12- Number of nodes in a MCP 4 network
In a network made as described in the previous paragraph, up to 32 MCP 4 may be installed, each one
publishing its data in order to make available them to the other components of the network. Since only one
MCP 4 at a time can access the RS485 communication line (COM2), being this of serial type, then the
publication of the information by all the components (or nodes) of the network needs a sure time.
Due to the particular management of the mechanism to access to the network, this time can be optimized
instructing each MCP 4 about how many are the participants to the same network; too do this, the following
directive has to be used:
NODESNUM
= ( num )
where
num
is the number of nodes and must be in the range 1 to 32.
The time required by all the nodes to publish their information, in the worst case of 125 Words to be
published, at 115.2 Kbaud, ranges from a minimum of 80 milliseconds, in the case of 2 MCP 4, to a
maximum of 1 second in the case of 32 MCP 4.
If the number of nodes has not been specified by the
NODESNUM
directive, this parameter will be set to 32 by
default; in this case the network will work anyway but, if for instance the network is made by 2 MCP 4, the
time needed for a full cycle will result increased from 80 milliseconds to 340 milliseconds (at 115.2 Kbaud
and in the worst case of 125 Words to be published).
The
NODESNUM
directive is thus optional, but it is useful to drastically reduce the time needed to exchange
data among MCP 4 controllers when the number of nodes is less than the allowed maximum value.
DUEMMEGI
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Rel.: 1.2 October 2018
Page 15 of 87
