Siemens RS-485 - Manual (Page 8)

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Siemens Building Technologies CC1A7865.1en
HVAC Products 31.10.2002
Writing n words
Slave
address
Function
0x10
Address
of first
word
Number of
words
Number of
bytes
(max. 2)
Word
value(s)
Check-
sum
CRC16
1 byte 1 byte 2 bytes 2 bytes 1 byte x byte(s) 2 bytes
Slave address Function 0x10 Address of
first word
Number of
words
Checksum
CRC16
1 byte 1 byte 2 bytes 2 bytes 2 bytes
Write switch-on threshold (Hys1 = -10)
Word address = 0x0018
Instruction:
0B 10 00 18 00 02 04 00 00 C1 20 CRC16
Reply:
0B 10 00 18 00 02 CRC16
The high byte must be transmitted first.
Example: Configuration code C111: “9030“
MOD bus: 0B10 0024 00 02 04 0903
The following explanations apply under the condition that the master works with the
IEEE-754 format. Before transmitting a value, the bytes must be exchanged in a way
that the order corresponds to the presentation for the MOD bus (see illustration below).
M-23 bit normalized mantissa
E-exponent (complement to base 2)
S-Sign-bit; 1 = negative, 0 = positive
MOD-Bus
Master
Re
ad
Wr
ite
MMMMMMMM MMMMMMMM SEEEEEEE EMMMMMMM
EMMMMMMM SEEEEEEE MMMMMMMM MMMMMMMM
(IEEE 754)
7865z13e/1102
Example:
Transmission of decimal value “550“:
MOD bus: 0x80, 0x00, 0x44, 0x09
Following is a description of all process values (variables) with their addresses, data
type and type of access.
Where:
R / O Read only access
R / W Read and write access
float Float value (4 bytes / 2 words)
word Integer (2 bytes / 1 word)
The process values are subdivided into logic areas.
Instruction
Reply
Example
Data type “char“
Data type “float“