LPC1768: SPI Programming

Objective

In this tutorial we are going to discuss the SPI ( Serial Peripheral Interface).
After understating the basics of LPC1768 SPI module, We will discuss how to use the Explore Embedded libraries to communicate with any of the SPI devices.

LPC1768 SPI Block

The below block diagram shows the SPI input pins multiplexed with other GPIO pins.
The SPI pin can be enabled by configuring the corresponding PINSEL register to select SPI function.
When the SPI function is selected for that pin in the Pin Select register, other Digital signals are disconnected from the SPI input pins.

Port Pin	PINSEL_FUNC_0	PINSEL_FUNC_1	PINSEL_FUNC_2	PINSEL_FUNC_3
P0.15	GPIO	TXD1	SCK0	SCK
P0.16	GPIO	RXD1	SSEL0	SSEL
P0.17	GPIO	CTS1	MISO0	MISO
P0.18	GPIO	DCD1	MOSI0	MOSI

SPI Registers

Register	Description
SPCR	SPI Control Register : used to configure SPI
SPSR	SPI status Register :
SPDR	SPI Data Register : contains received data or data to be transmitted
SPCCR	SPI Clock Counter Register : used to control master SCK frequency

SPCR
31:12	11:8	7	6	5	4	3	2	1: 0
RESERVED	BITS	SPIE	LSBF	MSTR	CPOL	CPHA	BIT ENABLE	RESERVED

Bit 1:0 – RESERVED

Bit 2 – BIT ENABLE:
This is used to clear the 16-byte Rx FIFO.
0-- .
1-- .

Bit 3 – CPHA:
0-- .
1-- .

Bit 4 – CPOL:
This is used for controlling clock polarity.
0 -- SCK is active high.
1 -- SCK is active low.

Bit 5 – MSTR:
This bit is used for Master mode select.
0 -- Slave Mode.
1 -- Master Mode.

Bit 6 – LSBF:
0 -- .
1 -- .

Bit 4 – SPIE:
This bit is used to enable SPI interrupt.
0 -- .
1 -- .

Bit 11:8 – BITS:
When bit 2 ( BIT ENABLE ) of this register is 1, this field controls the number of bits per transfer:
1000 -- 8 Bits per transfer
1001 -- 9 Bits per transfer
1010 -- 10 Bits per transfer
1011 -- 11 Bits per transfer
1100 -- 12 Bits per transfer
1101 -- 13 Bits per transfer
1110 -- 14 Bits per transfer
1111 -- 15 Bits per transfer
0000 -- 16 Bits per transfer

Bit 31:12 – RESERVED

SPSR
31:8	7	6	5	4	3	2 : 0
RESERVED	SPIF	WCOL	ROVR	MODF	ABRT	RESERVED

Bit 2:0 – RESERVED
Bit 3 – ABRT:
Bit 4 – MODF:
Bit 5 – ROVR:
Bit 6 – WCOL:
Bit 7 – SPIF:
Bit 31:8 – RESERVED:

SPDR
31:16	15:8	7: 0
RESERVED	Data High	Data Low

Bit 7:0 – Data Low :
Bit 15:8 – Data High :
Bit 31:16 – RESERVED

SPCCR
31:8	7 : 0
RESERVED	COUNTER

Bit 7:0 – COUNTER :
Bit 31:8 – RESERVED