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Fig.3
Fig.4
Fig.7
1 2 3
120 Ω
Reference guide for Modaer protocol
The Modaer communica on protocol is the communica on standard made available
by Aermec for the connec on 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 connec on (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 communica on 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 confi gura on:
•
•
Fig.6
•
•
Pin
Meaning
Data confi gura on:
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 fi elds 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 dura on of this interval depends on the baud rate.
The fi rst data to be transmi ed is the address of the machine; then the type of request
(read or write type), data rela ng 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 fi eld 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:
MAX 1000 mt
1.
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 opera on 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 transmi ed and is calculated from me to
me 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 informa on received is correct.
set the 16 bit checksum data with all 1 (0xff ff in hex)
run the Exor with the next byte of the message (star ng from the fi rst, i.e. the
address)
run the shi of a bit (toward the least signifi cant bit) by inser ng a 0 on the more
signifi cant bit
control on the least signifi cant bit extracted a er the shi (carry bit)
if the bit is 1 perform the exor with the fi xed data hex 0xA001
repeat the opera ons from point 3 un l 8 shi s have been made
repeat the opera ons from point 2 for each byte that comprises the message.
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