Vaisala HMM105 User Manual
TECHNICAL REFERENCE
I2C Protocol Implementation
HMM105 Humidity Module
M211638EN-A
PUBLISHED BY
Vaisala Oyj
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© Vaisala 2014
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Table of Contents
CHAPTER 1
GENERAL INFORMATION ............................................................................ 2
About This Manual ................................................................... 2
Version Information ................................................................. 2
Related Manuals ....................................................................... 2
CHAPTER 2
I2C INTERFACE ............................................................................................. 3
Overview ................................................................................... 3
Physical Interface .................................................................. 3
Communication Parameters .................................................. 4
Addressing ............................................................................ 4
Communication Flow ............................................................... 5
HMM105 State Machine ........................................................ 6
Examples of Communication Flow ........................................ 7
Timing .................................................................................... 9
Status Byte ............................................................................ 9
Checksum ............................................................................. 9
Status Word......................................................................... 10
Commands .............................................................................. 11
Get_Interface_Version ........................................................ 11
Get_Parameter .................................................................... 12
Example: Read RH Measurement Result ...................... 13
Set_Parameter .................................................................... 14
Example: Set Compensation Pressure .......................... 15
Get_Parameter_Info ............................................................ 16
Adjust .................................................................................. 17
Adjusting Measurement......................................................... 18
One Point Adjustment ......................................................... 18
Two Point Adjustment ......................................................... 18
Data Registers ........................................................................ 19
Data Formats .......................................................................... 19
Register Table ..................................................................... 20
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Technical Reference _________________________________________________________________
Manual Code
Description
M211638EN-A
May 2014. First version.
Manual Code
Manual Name
M211637EN
HMM105 Quick Guide
CHAPTER 1
GENERAL INFORMATION
About This Manual
This manual describes the I2C interface implementation of the
Vaisala HUMICAP® Humidity Module HMM105.
Version Information
Table 1 Manual Revisions
Related Manuals
Table 2 Related Manuals
2 _________________________________________________________________ M211638EN-A
Chapter 2 _______________________________________________________________ I2C Interface
3.3 V
5.0 V
SD
A
SCL
GND
2 x 10 kΩ
2 x 10 kΩ
uP
Bu
ffer and
level shi
ft
CHAPTER 2
I2C INTERFACE
Overview
HMM105 has an inter-integrated circuit (I2C) interface for interfacing
with the incubator’s control computer. HMM105 implements I2C slave
functionality, with the incubator’s computer acting as the master. The
interface can be used to read measurement values and status information,
set operation parameters, and make adjustments.
Physical Interface
The physical interface is a non-isolated 3-wire interface. Wires are SDA,
SCL and ground. SDA and SCL lines are buffered. Ground is shared
with power supply. There are small pull-up resistors for SCL and SDA.
Maximum cable length should not exceed 5 m and maximum capacitance
between communication lines and ground should not exceed 500 pF.
1405-072
Figure 1 Hardware Schematic
The physical connector is a Molex 87832-1007, 2 mm pitch shrouded
pin header with a locking window. It is marked X6 on the component
board. See Table 3 on page 4.
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Technical Reference _________________________________________________________________
Connector Pinout
Pin #
Function
6, 8
Supply voltage input
10 ... 35 VDC or 24 VAC
5, 7
Ground
1, 3
5 V I2C bus SDA
2, 4
5 V I2C bus SCL
0 1 0 1 1 1 1
R/W
Device type
Sub-address
Read/write bit
(LSB)
0 0 1 0 1 1 1 1 MSB
Device type
Sub-address
24
6810
1
3579
Table 3 HMM105 Signal and Power Connector X6
9, 10 Not connected
Communication Parameters
HMM105 supports a maximum clock speed of 50 kHz. Protocol bits are
sent most significant bit (MSB) first. Parameter bytes are sent using little
endian order.
Addressing
HMM105 uses 7-bit addressing. The address consists of:
- 4-bit device type identifier part (default “0101” for HMM105)
- 3-bit sub address (default “111”)
The full 7-bit default address is “0101111” (2Fh). In I2C communication,
the address should be provided by the master in the standard way after
the I2C start condition, with the read/write bit as the least significant bit
(LSB).
Table 4 HMM105 I2C Address
The I2C implementation of the HMM105 also includes the address inside
the message frame. The purpose of this is to make the I2C
implementation easier, since the I2C address can be lost by the I2C
hardware. This address is provided without the read/write bit, with zero
as the most significant bit (MSB).
Table 5 HMM105 Device Address
NOTE
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Make sure there are no addressing conflicts if other I2C devices are put
on the same bus. The HMM105 address can be changed, see Table 32 on
page 20.
Chapter 2 _______________________________________________________________ I2C Interface
This ACK/NACK refers to message level acknowlegde. I
includes separate byte level acknowledge.
Message Segment
Length
Content
Start
I2C start condition.
I2C address
1 byte
See Table 4 on page 4.
Command
1 byte
Identifier of command.
Device address
1 byte
See Table 5 on page 4.
Frame length
1 byte
Length of invoke message in bytes
Minimum invoke frame length is 5 bytes.
Data
Variable length
Content and length depending on the
contains no data in the invoke message.
Checksum
2 bytes
See section Checksum on page 9.
Stop
I2C stop condition
Message Segment
Length
Content
Start
I2C start condition.
I2C address
1 byte
See Table 4 on page 4.
Status
1 byte
See section Status Byte on page 9.
Command
1 byte
Identifier of the command that was used
valid invoke), command code is FFh.
Device address
1 byte
See Table 5 on page 4.
Frame length
1 byte
Length of the response message in
length is 6 bytes.
Data
Variable length
Content and length depending on the
command.
Checksum
2 bytes
See section Checksum on page 9.
Stop
I2C stop condition
Communication Flow
Basic communication flow always includes I2C write and read
commands. First the master writes a command to the slave device, and
then the master reads the results of that command from the slave.
When the master reads data from the slave, there is an ACK/NACK-bit in
the status byte that informs the master whether or not communication
was success. ACK is defined as zero and NACK is defined as one in the
logical level.
2
NOTE
Command messages sent by the master are called invokes. Replies sent
by the slave are called responses. Note that also responses include the
device address.
Table 6 Invoke Message in HMM105 I2C Interface
C protocol
(excluding I2C address, including CRC).
command. May be left out if command
Table 7 Response Message in HMM105 I2C Interface
in the invoke that the slave is
responding to. If slave is in idle state (no
bytes (excluding I2C address, including
CRC). The minimum response frame
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