User's Manual

Cinterion
®
ELS61-AUS Hardware Interface Description
2.1 Application Interface
52
 ELS61-AUS_HID_v00.031 2016-06-03
Confidential / Preliminary
Page 37 of 102
2.1.10 SPI Interface
Four ELS61-AUS GPIO interface lines can be configured as Serial Peripheral Interface (SPI).
The SPI is a synchronous serial interface for control and data transfer between ELS61-AUS
and the external application. Only one application can be connected to the SPI and the inter-
face supports only master mode. The transmission rates are up to 6.5Mbit/s. The SPI interface
comprises the two data lines MOSI and MISO, the clock line SPI_CLK a well as the chip select
line SPI_CS.
The four GPIO lines can be configured as SPI interface signals as follows: GPIO3 --> SPI_CLK,
GPIO16 --> MOSI, GPIO17 --> MISO and GPIO19 --> SPI_CS. The configuration is done by
AT command (see [1]). It is non-volatile and becomes active after a module restart.
The GPIO lines are also shared with the ASC1 signal lines and the ASC0 modem status signal
line DSR0.
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
MOSI
SPI_CLK
MISO
SPI_CS
MOSI
SPI_CLK
MISO
SPI_CS
MOSI
SPI_CLK
MISO
SPI_CS
MOSI
SPI_CLK
MISO
Sample Sample
Sample Sample