Datasheet

Preliminary Data Sheet
BMA400
Page 124 /
Confidential
BST-BMA400-DS000-00 | Version 0.1 | November 2017 Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
6.2. Interface I2C/SPI Protocol Selection
The protocol is automatically selected based on the chip select CSB pin behavior after power-up.
At reset / power-up, BMA400 is in I2C mode. If CSB is connected to VDDIO during power-up and not
changed the sensor interface works in I2C mode. For using I2C, it is recommended to hard-wire the
CSB line to VDDIO. Since power-on-reset is only executed when both VDD and VDDIO are
established, there is no risk of incorrect protocol detection due to power-up sequence.
If CSB sees a rising edge after power-up, the BMA400 interface switches to SPI until a reset or the
next power-up occurs. Therefore, a CSB rising edge is needed before starting the SPI communication.
Hence, it is mandatory to perform a SPI single read of e.g. register CHIP_ID (the obtained value will
be invalid) before the actual communication start, in order to use the SPI interface.
6.3. SPI interface and protocol
The timing specification for SPI of the BMA400 is given in the following table:
SPI timing, valid at V
DDIO
≥ 1.71V
Parameter
Symbol
Condition
Min
Max
Units
Clock Frequency
f
SPI
Max. Load on
SDI or SDO =
25pF, V
DDIO
≥
1.71 V
10
MHz
V
DDIO
< 1.71V
6
MHz
SCK Low Pulse
t
SCKL
48
ns
SCK High Pulse
t
SCKH
48
ns
SDI Setup Time
t
SDI_setup
20
ns
SDI Hold Time
t
SDI_hold
20
ns
SDO Output Delay
t
SDO_OD
Load = 30pF,
V
DDIO
≥ 1.62V
30
ns
CSB Setup Time
t
CSB_setup
20
ns
CSB Hold Time
t
CSB_hold
40
ns
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