Nxp Semiconductors UM10237 ユーザーズマニュアル

UM10237_2

© NXP B.V. 2008. All rights reserved.

If the SSEL signal goes active, when the SPI block is a master, this indicates another 
master has selected the device to be a slave. This condition is known as a mode fault. 
When a mode fault is detected, the mode fault (MODF) bit in the status register will be 
activated, the SPI signal drivers will be de-activated, and the SPI mode will be changed to 
be a slave.

If the Px.y/SSEL/... pin is assigned the SSEL function in Pin Function Select Register 0, 
the SSEL signal must always be inactive when the SPI controller is a master.

A slave transfer is considered to be aborted, if the SSEL signal goes inactive before the 
transfer is complete. In the event of a slave abort, the transmit and receive data for the 
transfer that was in progress are lost, and the slave abort (ABRT) bit in the status register 
will be activated.

 

SCK

Input/ 
Output

 The SPI is a clock signal used to synchronize the transfer of data 

across the SPI interface. The SPI is always driven by the master and received 
by the slave. The clock is programmable to be active high or active low. The SPI 
is only active during a data transfer. Any other time, it is either in its inactive 
state, or tri-stated.

SSEL

Input

 The SPI slave select signal is an active low signal that indicates 

which slave is currently selected to participate in a data transfer. Each slave has 
its own unique slave select signal input. The SSEL must be low before data 
transactions begin and normally stays low for the duration of the transaction. If 
the SSEL signal goes high any time during a data transfer, the transfer is 
considered to be aborted. In this event, the slave returns to idle, and any data 
that was received is thrown away. There are no other indications of this 
exception. This signal is not directly driven by the master. It could be driven by a 
simple general purpose I/O under software control.

On the LPC2400 (unlike earlier NXP ARM devices) the SSEL pin can be used 
for a different function when the SPI interface is only used in Master mode. For 
example, pin hosting the SSEL function can be configured as an output digital 
GPIO pin and used to select one of the SPI slaves.

MISO

Input/ 
Output

 The MISO signal is a unidirectional signal used to transfer 

serial data from the slave to the master. When a device is a slave, serial data is 
output on this signal. When a device is a master, serial data is input on this 
signal. When a slave device is not selected, the slave drives the signal high 
impedance.

MOSI

Input/ 
Output

 The MOSI signal is a unidirectional signal used to transfer 

serial data from the master to the slave. When a device is a master, serial data 
is output on this signal. When a device is a slave, serial data is input on this 
signal.