Fig.3
Fig.4
Fig.7
1 2 3
120 Ω
Reference guide for Modaer protocol
The Modaer communication protocol is the communication standard made available
by Aermec for the connection between chillers and centralised supervision or control
systems (see the Aermec products guide to see on which machine this protocol is avail-
able).
The protocol allows both the point to point connection (machine * supervisor), as well as
Fig.5
several machines (max 255) on the same bus link to a supervisor, because it manages one
address for each machine.
The system uses a master-slave communication mode, therefore the supervision system
is master and the machine slave.
1 2 3
This means that the machine only responds to the enquiry made by the supervisor.
Serial configuration:
•
•
Fig.6
•
•
Pin
Meaning
Data configuration:
Meaning
Each 8 bit word (1 byte) in the message is comprised of two coded
hex characters with 4 bits each (0-9, A-F).
1
GND
2
RX+/TX+
Message format:
3
RX-/TX
The fields that comprise the message are shown in Table 1.
The message begins with a dead interval of at least 3.5 characters long (indicated in
Table 1 as a dead period).
The duration of this interval depends on the baud rate.
The first data to be transmitted is the address of the machine; then the type of request
(read or write type), data relating to the request, the checksum and then a dead inter-
val with the same length as that at the beginning .
Tab.1
START
ADDRESS
COMMAND
DATA
CHECKSUM
SHigh
Address:
Command:
Checksum:
The checksum is calculated by considering all areas except the checksum field and consid-
ering only the 8 bits of data for each byte (excluding start and shigh bits).
The checksum is a 16-bit data and is obtained as as follows:
1.
MAX 1000 mt
2.
3.
4.
5.
6.
7.
1200 to 19200 baud
1 start bit
no parity
2 shigh bits
dead time
1 byte
1 byte
n x byte
2 bytes
dead time
this is the machine address and can be comprised
between 1 and 255.
this is the operation you want to perform, the list is in
"Tab.2. page 2 "
this is a safety check to verify the correctness of the
data being transmitted and is calculated from time to
time by the sender of the message; the receiver has
to recalculate and compare it with the one received in
order to be sure that all information received is correct.
set the 16 bit checksum data with all 1 (0xffff in hex)
run the Exor with the next byte of the message (starting from the first, i.e. the
address)
run the shift of a bit (toward the least significant bit) by inserting a 0 on the more
significant bit
control on the least significant bit extracted after the shift (carry bit)
if the bit is 1 perform the exor with the fixed data hex 0xA001
repeat the operations from point 3 until 8 shifts have been made
repeat the operations from point 2 for each byte that comprises the message.
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