MMA955xL
Sensors
10 Freescale Semiconductor, Inc.
3.3 Pin Function Descriptions
This section provides a brief description of the various pin functions available on the MMA955xL platform. Ten of the device pins
are multiplexed with Rapid GPIO (RGPIO) functions. The “Pin Function #1” column in Table 3 on page 9 lists which function is
active when the hardware exits the Reset state. Freescale or user firmware can use the pin mux-control registers in the System
Integration Module (SIM) to change pin assignments for each pin after reset. For detailed information about these registers, see
the MMA955xL Three-Axis Accelerometer Reference Manual (MMA955xLRM).
V
DD
and V
SS
: Digital power and ground. V
DD
is nominally 1.8 V.
V
DDA
and V
SSA
: Analog power and ground. V
DDA
is nominally 1.8 V. To optimize performance, the V
DDA
line can be filtered to
remove any digital noise that can be present on the 1.8 V supply. (See Figure 5 and Figure 6 on page 16.)
RESETB: The RESETB pin is an open-drain, bidirectional pin with an internal, weak, pullup resistor. At start-up, it is configured
as an input pin, but also can be programmed to become bidirectional. Using this feature, the MMA955xL device can reset external
devices for any purpose other than power-on reset. Reset must be pulled high at power up to boot to Application code space. If
low, it will boot to ROM code. After startup, Reset may be asserted to reset the device. The total external capacitance to ground
has to be limited when using RESETB-pin, output-drive capability. For more details, see the “System Integration Module” chapter
of the MMA955xL Three-Axis Accelerometer Reference Manual (MMA955xLRM).
Slave I
2
C port: SDA0 and SCL0: These are the slave-I
2
C data and clock signals, respectively. The MMA955xL device can be
controlled via the serial port or via the slave SPI interface.
Master I
2
C: SDA1 and SCL1: These are the master-I
2
C data and clock signals, respectively.
Analog-to-Digital Conversion: AN0, AN1: The on-chip ADC can be used to perform a differential, analog-to-digital conversion
based on the voltage present across pins AN0(-) and AN1(+). Conversions for these pins are at the same Output Data Rate
(ODR) as the MEMS transducer signals. Input levels are limited to 1.8 V differential.
Rapid General Purpose I/O: RGPIO[9:0]: The CPU has a feature called Rapid GPIO (RGPIO). This is a 16-bit, input/output port
with single-cycle write, set, clear, and toggle functions available to the CPU. The MMA955xL device brings out the lower 10 bits
of that port as pins of the device. At reset, All of the RGPIO pins are configured as input pins, although pin muxing does reassign
some pins to non-RGPIO function blocks. Pull-ups are disabled.
RGPIO[9] is connected to BKGD/MS. RGPIO[9:6] can be set as interrupt pins for most interrupt sources.
RGPIO[1:0] SDA0 and SCL0 are connected at reset.
Interrupts: INT: This input pin can be used to wake the CPU from a deep-sleep mode. It can be programmed to trigger on either
rising or falling edge, or high or low level. This pin operates as a Level-7 (high-priority) interrupt.
Debug/Mode Control: BKGD/MS: At start-up, this pin operates as mode select. If this pin is pulled high during start up, the CPU
will boot normally and run code. If this pin is pulled low during start-up, the CPU will boot into active Background-Debug Mode
(BDM). In BDM, this pin operates as a bidirectional, single-wire, background-debug port. It can be used by development tools for
downloading code into on-chip RAM and flash and to debug that code. There is an internal pullup resistor on this pin. It may be
left floating.
Timer: PDB_A and PDB_B: These are the two outputs of the programmable delay block.
Slave SPI Interface: SCLK, SDI, SDO and SSB: These pins control the slave SPI clock, data in, data out, and slave-select
signals, respectively. The MMA955xL platform can be controlled via this serial port or via the slave-I
2
C interface. SSB has a spe-
cial function at startup that selects the Slave interface mode. Low at startup selects SPI and high selects I
2
C.
INT_O: The slave-port output interrupt pin. This pin can be used to flag the host when a response to a command is available to
read on the slave port. This Interrupt pin can only output the COCO bit interrupt. Other than for the MMA9559, use RGPIO6–
RGPIO9 for full interrupt capability.
TPMCH0 and TPMCH1: The I/O pin associated with 16-bit, TPM channel 0 and 1.
3.4 System Connections
3.4.1 Power Sequencing
An internal circuit powered by V
DDA
provides the device with a power-on-reset signal. In order for this signal to be properly rec-
ognized, it is important that V
DD
is powered up before or simultaneously with V
DDA
. The voltage potential between V
DD
and V
DDA
must not be allowed to exceed the value specified in Table 7 on page 16.
3. RGPIO3/SDA1/SSB = Low at startup selects SPI. High at startup selects I
2
C. This is a function of the application boot code, not of the hardware.
