Vaisala HUMICAP HMM105 Use and care manual

TECHNICAL REFERENCE
I2C Protocol Implementation
HMM105 Humidity Module
M211638EN-C

PUBLISHED BY
Vaisala Oyj
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VAISALA _____________________________________________________________________ 1
Table of Contents
CHAPTER 1
GENERAL INFORMATION............................................................................ 2
About This Document .............................................................. 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

Technical Reference_________________________________________________________________
2 _________________________________________________________________ M211638EN-C
CHAPTER 1
GENERAL INFORMATION
About This Document
This document describes the I2C interface implementation of the
Vaisala HUMICAP®Digital Humidity Module HMM105.
Version Information
Table 1 Document Versions
Document Code
Description
M211638EN-C
November 2019. Updated Table 16, Table 21, and
Table 32.
M211638EN-B
December 2015. Updated description of checksum
calculation.
M211638EN-A
May 2014. First version.
Related Manuals
Table 2 Related Manuals
Document Code
Name
M211637EN
Vaisala HUMICAP®Digital Humidity Module HMM105
Quick Reference Guide

Chapter 2 _______________________________________________________________ I2C Interface
VAISALA _____________________________________________________________________ 3
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 below.
Table 3 HMM105 Signal and Power Connector X6
Connector Pinout
Pin #
Function
6, 8
Supply voltage input
3.3 V5.0 V
SDA
SCL
GND
2 x 10 kΩ2 x 10 kΩ
uP
Buffer and
level shift

Technical Reference_________________________________________________________________
4 _________________________________________________________________ M211638EN-C
10 ... 35 VDC or 24 VAC
5, 7
Ground
1, 3
5 V I2C bus SDA
2, 4
5 V I2C bus SCL
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
0
1
0
1
1
1
1
R/W
Device type
Sub-address
Read/write bit
(LSB)
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
0
0
1
0
1
1
1
1
MSB
Device type
Sub-address
NOTE
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
.
2
4
6
8
10
1
3
5
7
9

Chapter 2 _______________________________________________________________ I2C Interface
VAISALA _____________________________________________________________________ 5
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.
NOTE
This ACK/NACK r
efers to message level acknowledge. I2C protocol
includes separate byte level acknowledge.
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
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
(excluding I2C address, including CRC).
Minimum invoke frame length is 5 bytes.
Data
Variable length
Content and length depending on the
command. May be left out if command
contains no data in the invoke message.
Checksum
2 bytes
See section Checksum on page 9.
Stop
I2C stop condition
Table 7 Response Message in HMM105 I2C Interface
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
in the invoke that the slave is
responding to. If slave is in idle state (no
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
bytes (excluding I2C address, including
CRC). The minimum response frame
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

Technical Reference_________________________________________________________________
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HMM105 State Machine
The main and initial state of the HMM105 is Idle, and it will change to
WaitResponse state only when a valid invoke is received. In
WaitResponse state HMM105 expects to see an I2C read operation. After
seeing a read operation the HMM105 outputs its response with
ACK/NACK and status signals.
If HMM105 is in WaitResponse state and the master sends a new invoke,
the old response belonging to the old invoke will be lost. When the
master sends the next I2C read command, the HMM105 sends it the
response to the latest invoke.
If HMM105 is in Idle state and I2C read is sent, HMM105 responds with
a NACK-signal. This tells the master that the data which the master may
have received in same I2C read is not valid.
If the HMM105 receives an invalid invoke, it goes to the Idle state. An
invoke message can be invalid because of an unknown command,
erroneous CRC, or invalid message length.
.
1405-073
Figure 2 HMM105 State Machine
Wait
Response
Idle
Valid Invoke
Valid Invoke
Response
NACK
Response
ACK +data
Bad Invoke
Bad Invoke
Response
NACK

Chapter 2 _______________________________________________________________ I2C Interface
VAISALA _____________________________________________________________________ 7
Examples of Communication Flow
The basic data transfer communication flows are presented in the
following figures. Each arrow represents an I2C read or write operation
The examples are simplified presentations. For actual message content,
see section Commands on page 11.
For example, Figure 3 below shows the following message sequence:
1. The master invokes the Get_Parameter command to read the RH
parameter using an I2C write operation. This command prepares the
slave to wait for a read operation from the master.
2. The master begins an I2C read operation to read the results of the
Get_Parameter RH command. The slave sends the requested RH
result and an ACK signal to the master.
1401-020
Figure 3 Get_Parameter with ACK
1401-032
Figure 4 Set_Parameter with ACK
Master
Slave
Get_Parameter,RH_ID
I2C write
Get_Parameter,RH_ID,54.32,ACK
I2C read
Master
Slave
Set_Parameter,Pressure_ID,1013.25
I2C Write
Set_Parameter,Pressure_ID,ACK
I2C Read

Technical Reference_________________________________________________________________
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1401-022
Figure 5 Get_Parameter with NACK
1401-021
Figure 6 Get_Parameter with Alarm
NOTE
Alarm can be any of the state bits in status byte.
Master
Slave
Get_Parameter,RH_ID
I2C Write
Get_Parameter,RH_ID,nan,NACK
I2C Read
Master
Slave
Get_Parameter,RH_ID
I2C Write
Get_Parameter,RH_ID,66.55,Alarm bit = 1, ACK
I2C Read
Get_Parameter,Status_ID
I2C Write
Get_Parameter,Status_ID,statusword,ACK
I2C Read