Vaisala HMM105 - Manual (Page 5)

Chapter 2 _______________________________________________________________ I2C Interface
VAISALA _____________________________________________________________________ 3
CHAPTER 2
I
2
C INTERFACE
Overview
HMM105 has an inter-integrated circuit (I 2 C) interface for interfacing
with the incubator’s control computer. HMM105 implements I 2 C 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.
3.3 V 5.0 V
SDA
SCL
GND
2 x 10 kΩ 2 x 10 kΩ
uP
Buffer and
level shift