I 2 C Simplified Protocol - E+E Elektronik EE895 User Manual

The I C interface encapsulates the data according Modbus PDU packets, including CRC:
2
S Slave Address
S Slave Address
Every byte of the Modbus PDU and the Modbus CRC must be acknowledged
(according to I C specification, not shown above).
2
The EE895 module supports repeated START or STOP conditions between the request packet and the
response packet. If a START condition and an address match are detected, the EE895 will stay active
until a STOP condition is received or an idle timeout of 500 ms occurs. This might increase the power
consumption and self-heating. The I
le in case of a repeated START.
The CRC16 shall be calculated including the slave address. For the Modbus register map please refer
to chapter 4.3, page 14. For Modbus specifications, please refer to Appendix 1, page 18.
Example of command reading the temperature (floating point value) T = 27.50 °C from the register 0x3EA:
Request [Hex]: S BE 03 03 EA 00 02 E8 C5 P
Slave address
START
7-bit shifted
S BE
Response [Hex]: S BF 03 04 00 00 41 DC 74 3F P
Slave address
START
7-bit shifted
S BF
For decoding of float values stored according standard IEEE754, please refer to Appendix 1, page 18.
Example of Decoding:
Response [Hex]:
Byte 1
(Register 2 - Hi)
41
Please note: For obtaining the correct value, both registers have to be read within the same reading
cycle. The measured value can change between two Modbus requests, therefore, exponent and
mantissa may get inconsistent.
4.1.2 I C Simplified Protocol
2
I C slave adress: 0x5E
2
This I²C protocol is intended for I
"EEPROM-like-mode".
The simplified I
in 8 subsequent registers, as 16 bit integers.
Slave address
0x5E
*) reserved for future use
12
W A Request: Modbus PDU + Modbus CRC
R A Response: Modbus PDU + Modbus CRC
C master shall ensure that the data is retrieved as soon as possib-
2
Function Starting
code address Hi
03
Function Byte
code count
03 04
Byte 2
(Register 2 – Lo)
DC
C master reading the measured values from EE895 in
2
C does not support any error detection (such as CRC) and provides the measured data
2
0x00 0x01
CO CO
2 2
high byte low byte
Starting No. of
address Lo register Hi
03 EA
Register 1 Register 1
value Hi value Lo
00 00
Byte 3
(Register 1 - Hi)
00
0x02 0x03
T T reserved*)
high byte low byte high byte
User Manual EE895 Miniature Sensor Module for CO
No. of
register Lo
00 02 E8
Register 2 Register 2
value Hi value Lo
41 DC 74
Byte 4
(Register 1 - Lo)
00
0x04 0x05 0x06
reserved*)
low byte high byte
P
P
CRC STOP
C5 P
CRC STOP
3F P
Decimal value
27.50
0x07
p p
low byte
, T and p
2