Philips LPC213 Series User Manual page 149

Philips Semiconductors
Volume 1
When a device is a slave, and CPHA is set to 0, the transfer starts when the SSEL signal
goes active, and ends when SSEL goes inactive. When a device is a slave, and CPHA is
set to 1, the transfer starts on the first clock edge when the slave is selected, and ends on
the last clock edge where data is sampled.
12.2.3 General information
There are four registers that control the SPI peripheral. They are described in detail in
Section 12.4 "Register description" on page
The SPI control register contains a number of programmable bits used to control the
function of the SPI block. The settings for this register must be set up prior to a given data
transfer taking place.
The SPI status register contains read only bits that are used to monitor the status of the
SPI interface, including normal functions, and exception conditions. The primary purpose
of this register is to detect completion of a data transfer. This is indicated by the SPIF bit.
The remaining bits in the register are exception condition indicators. These exceptions will
be described later in this section.
The SPI data register is used to provide the transmit and receive data bytes. An internal
shift register in the SPI block logic is used for the actual transmission and reception of the
serial data. Data is written to the SPI data register for the transmit case. There is no buffer
between the data register and the internal shift register. A write to the data register goes
directly into the internal shift register. Therefore, data should only be written to this register
when a transmit is not currently in progress. Read data is buffered. When a transfer is
complete, the receive data is transferred to a single byte data buffer, where it is later read.
A read of the SPI data register returns the value of the read data buffer.
The SPI clock counter register controls the clock rate when the SPI block is in master
mode. This needs to be set prior to a transfer taking place, when the SPI block is a master.
This register has no function when the SPI block is a slave.
The I/Os for this implementation of SPI are standard CMOS I/Os. The open drain SPI
option is not implemented in this design. When a device is set up to be a slave, its I/Os are
only active when it is selected by the SSEL signal being active.
12.2.4 Master operation
The following sequence describes how one should process a data transfer with the SPI
block when it is set up to be the master. This process assumes that any prior data transfer
has already completed.
User manual
1. Set the SPI clock counter register to the desired clock rate.
2. Set the SPI control register to the desired settings.
3. Write the data to transmitted to the SPI data register. This write starts the SPI data
transfer.
4. Wait for the SPIF bit in the SPI status register to be set to 1. The SPIF bit will be set
after the last cycle of the SPI data transfer.
5. Read the SPI status register.
6. Read the received data from the SPI data register (optional).
7. Go to step 3 if more data is required to transmit.
Rev. 01 — 24 June 2005
151.
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
UM10120
Chapter 12: SPI
149