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AC75 Hardware Interface Description

Strictly confidential / Preliminary

AC75_HD_V00.202 Page 61 of 120 27.04.2006

3.14 SPI Interface

The SPI (serial peripheral interface) is a synchronous serial interface for control and data

transfer between the AC75 module and the connected application. Only one application can

be connected to the module’s SPI. The interface supports transmission rates up to 6.5Mbit/s.

It consists of four lines, the two data lines SPIDI/SPIDO, the clock line SPICLK and the chip

select line SPICS.

The AC75 module acts as a single master device, e.g. the clock SPICLK is driven by module.

Whenever the SPICS pin is in a low state, the SPI bus is activated and data can be

transferred from the module and vice versa. The SPI interface uses two independent lines for

data input (SPIDI) and data output (SPIDO).

GSM module Application

SPICLK SPICLK

SPICS

SPIDO

SPIDI SPIDI

SPIDO

Figure 21: SPI interface

To configure and activate the SPI bus use the AT^SSPI command. If the SPI bus is active

the two lines I2CCLK and I2DAT are locked for use as I

C lines. Detailed information on the

AT^SSPI command as well explanations on the SPI modes required for data transmission

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 22 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 26.

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Siemens AC75 Specifiche Pagina 61