User's Manual Part 1

MC75 Hardware Interface Description
Strictly confidential / Draft
s
MC75_V00.190a Page 46 of 91 15.02.2005
3.10 I
2
C Interface
I
2
C is a serial, 8-bit oriented data transfer bus for bit rates up to 400 kbps in Fast mode. It
consists of two lines, the serial data line I2CDAT and the serial clock line I2CCLK.
The MC75 module acts as a single master device, e.g. the clock I2CCLK is driven by
module. I2CDAT is a bi-directional line.
Each device connected to the bus is software addressable by a unique address, and simple
master/slave relationships exist at all times. The module operates as master-transmitter or as
master-receiver. The customer application transmits or receives data only on request of the
module. To configure and activate the I
2
C interface use the AT^SSPI command described in
[1].
The I
2
C interface can be powered from an external supply or via the VEXT line of MC75. If
connected to the VEXT line the I
2
C interface will be properly shut down when the module
enters the Power-down mode. If you prefer to connect the I
2
C interface to an external power
supply, take care that VCC of the application is in the range of V
VEXT
and that the interface is
shut down when the PWR_IND signal goes high. See figures below as well as Section 7 and
Figure 39.
In the application I2CDAT and I2CCLK lines need to be connected to a positive supply
voltage via a pull-up resistor.
For electrical characteristics please refer to Table 16.
GSM module
I2DAT
I2CCLK
GND
I2DAT
I2CCLK
GND
Application
VCC
R
p
R
p
w
VEXT
Figure 15: I
2
C interface connected to VCC of application
GSM module
I2DAT
I2CCLK
GND
I2DAT
I2CCLK
GND
Application
VEXT
R
p
R
p
Figure 16: I
2
C interface connected to VEXT line of MC75
Note: Good care should be taken when creating the PCB layout of the host application: The
traces of I2CCLK and I2CDAT should be equal in length and as short as possible.