User's Manual

Cinterion
®
ELS31-VA/ELS51-VA Hardware Interface Description
2.1 Application Interface
56
 ELS31-VA_ELS51-VA_HID_v01.000 2017-01-04
Confidential / Preliminary
Page 38 of 106
2.1.12 SPI Interface
The ELS31-VA/ELS51-VA GPIO interface lines can be configured as Serial Peripheral Inter-
face (SPI). The SPI is a synchronous serial interface for control and data transfer between
ELS31-VA/ELS51-VA and the external application. Only one application can be connected to
the SPI and the interface supports only master mode. The transmission rates are up to 6.5Mbit/
s. The SPI interface comprises the two data lines SPI_MOSI and SPI_MISO, the clock line
SPI_CLK a well as the chip select lines SPI_CS1 and SPI_CS2.
These two GPIO lines can be configured as SPI interface signals as follows: GPO26 -->
SPI_CS1 and GPIO27 --> SPI_CS2. The configuration is done by AT command (see [1]). It is
non-volatile and becomes active after a module restart.
To configure and activate the SPI interface use the AT^SSPI command. Detailed information
on the AT^SSPI command as well explanations on the SPI modes required for data transmis-
sion can be found in [1].
In general, SPI supports four operation modes. The modes are different in clock phase and
clock polarity. The module’s SPI mode can be configured by using the AT command AT^SSPI.
Make sure the module and the connected slave device works with the same SPI mode.
Figure 16 shows the characteristics of the four SPI modes. The SPI modes 0 and 3 are the most
common used modes. For electrical characteristics please refer to Table 2.
Figure 16: Characteristics of SPI modes
SPI MODE 0 SPI MODE 1
SPI MODE 2 SPI MODE 3
Clock phase
Clock polarity
SPI_CS
SPI_MOSI
SPI_CLK
SPI_MISO
SPI_CS
SPI_MOSI
SPI_CLK
SPI_MISO
SPI_CS
SPI_MOSI
SPI_CLK
SPI_MISO
SPI_CS
SPI_MOSI
SPI_CLK
SPI_MISO
Sample Sample
Sample Sample