UM10462
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User manual
Rev. 5.5 — 21 December 2016
289 of 523
NXP Semiconductors
UM10462
Chapter 13: LPC11U3x/2x/1x SSP/SPI
turn latches each bit on the rising edge of SK. At the end of the frame, for single transfers,
the CS signal is pulled HIGH one clock period after the last bit has been latched in the
receive serial shifter, that causes the data to be transferred to the receive FIFO.
Note:
The off-chip slave device can tri-state the receive line either on the falling edge of
SK after the LSB has been latched by the receive shiftier, or when the CS pin goes HIGH.
For continuous transfers, data transmission begins and ends in the same manner as a
single transfer. However, the CS line is continuously asserted (held LOW) and
transmission of data occurs back to back. The control byte of the next frame follows
directly after the LSB of the received data from the current frame. Each of the received
values is transferred from the receive shifter on the falling edge SK, after the LSB of the
frame has been latched into the SSP/SPI.
13.7.3.1 Setup and hold time requirements on CS with respect to SK in Microwire
mode
In the Microwire mode, the SSP/SPI slave samples the first bit of receive data on the
rising edge of SK after CS has gone LOW. Masters that drive a free-running SK must
ensure that the CS signal has sufficient setup and hold margins with respect to the rising
edge of SK.
illustrates these setup and hold time requirements. With respect to the SK rising
edge on which the first bit of receive data is to be sampled by the SSP/SPI slave, CS must
have a setup of at least two times the period of SK on which the SSP/SPI operates. With
respect to the SK rising edge previous to this edge, CS must have a hold of at least one
SK period.
Fig 39. Microwire frame format setup and hold details
SK
CS
SI
t
HOLD
= t
SK
t
SETUP
=2*t
SK