PIC32MX: SPI Communication between PIC32s - Revision history

NickMarchuk at 20:17, 1 March 2010

2010-03-01T20:17:50Z

← Older revision		Revision as of 15:17, 1 March 2010
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	== Original Assignment ==

	'''Do not erase this section!'''

	Your assignment is to create code that allows two PIC32 boards to communicate with each other via SPI.

	== Overview ==		== Overview ==

JamesRein: /* Overview */

2010-02-16T04:31:44Z

Overview

← Older revision		Revision as of 23:31, 15 February 2010
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	SPI or [http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus Serial Peripheral Interface] is a communication method that was once used to connect devices such as printers, cameras, scanners, etc. to a desktop computer. This function has largely been taken over by USB, but SPI can still be a useful communication tool for some applications. SPI runs using a master/slave set-up and can run in full duplex mode, meaning that signals can be transmitted between the master and the slave simultaneously. There is no standard communication protocol for SPI.		SPI or [http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus Serial Peripheral Interface] is a communication method that was once used to connect devices such as printers, cameras, scanners, etc. to a desktop computer. This function has largely been taken over by USB, but SPI can still be a useful communication tool for some applications. SPI runs using a master/slave set-up and can run in full duplex mode, meaning that signals can be transmitted between the master and the slave simultaneously. There is no standard communication protocol for SPI.

	SPI is still used to control some peripheral devices and has some advantages over [[~~I2C communication between PICs~~\|I2C]]~~'''CHANGE THIS TO OUR I2C PAGE!!'''~~ (another type of serial data communication). SPI can communicate at much higher data rates than I2C. Furthermore, when multiple slaves are present, SPI requires no addressing to differentiate between these slaves. Compared to parallel buses, SPI has the additional benefit of requiring only simple wiring. However, one disadvantage when compared to I2C is that each slave must have a dedicated slave line. A slave line is not necessary when only one slave is present.		SPI is still used to control some peripheral devices and has some advantages over [[PIC32MX:_I2C_Communication_between_PIC32s\|I2C]] (another type of serial data communication). SPI can communicate at much higher data rates than I2C. Furthermore, when multiple slaves are present, SPI requires no addressing to differentiate between these slaves. Compared to parallel buses, SPI has the additional benefit of requiring only simple wiring. However, one disadvantage when compared to I2C is that each slave must have a dedicated slave line. A slave line is not necessary when only one slave is present.

JamesRein: /* Code */

2010-02-16T04:28:56Z

Code

← Older revision		Revision as of 23:28, 15 February 2010
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	No slave select line is used since there is only one slave, but if there were multiple slaves it would have to be used.		No slave select line is used since there is only one slave, but if there were multiple slaves it would have to be used.
	The SPI module sends and receives at the same time, so whenever a byte is written to SPI1BUF the module immediately sends out that byte on SDO which clocking with SCK and a byte is clocked in at the same time and written back to SPI1BUF. The send and receive buffers, SPI1TXB and SPI1RXB, cannot be written to directly, but instead are memory mapped to SPI1BUF. If the slave is not sending a value back when the master sends a byte, a 0x00 will be written into SPI1BUF. Because of this, in the code below the master reads from SPI1BUF after sending to clear the buffer and prevent overflow. To actually receive a byte, the master ''must'' send a byte as well. In the code below, by writing a zero to SPI1BUF, the master clocks out zero and in the slave message at the same time, at which point the slave message can be used. Since SPI is slower than the system clock, reading from SPI1BUF immediately would not result in the correct byte, instead the pic must wait for the module to finish sending, which the function getcSPI1() does automatically. Similarly, the slave sends a byte back by writing a value into SPI1BUF, but since the module is in slave mode the clock is not generated immediately. Instead the value waits in SPI1TXB until the clock is generated by the master. At this point the slave clocks out that value and in another value.		The SPI module sends and receives at the same time, so whenever a byte is written to SPI1BUF the module immediately sends out that byte on SDO which clocking with SCK and a byte is clocked in at the same time and written back to SPI1BUF. The send and receive buffers, SPI1TXB and SPI1RXB, cannot be written to directly, but instead are memory mapped to SPI1BUF. If the slave is not sending a value back when the master sends a byte, a 0x00 will be written into SPI1BUF. Because of this, in the code below the master reads from SPI1BUF after sending to clear the buffer and prevent overflow. To actually receive a byte, the master ''must'' send a byte as well. In the code below, by writing a zero to SPI1BUF, the master clocks out zero and in the slave message at the same time, at which point the slave message can be used. Since SPI is slower than the system clock, reading from SPI1BUF immediately would not result in the correct byte, instead the pic must wait for the module to finish sending, which the function getcSPI1() does automatically. Similarly, the slave sends a byte back by writing a value into SPI1BUF, but since the module is in slave mode the clock is not generated immediately. Instead the value waits in SPI1TXB until the clock is generated by the master. At this point the slave clocks out that value and in another value.

JamesRein: /* Overview */

2010-02-16T03:07:30Z

Overview

← Older revision		Revision as of 22:07, 15 February 2010
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	The master, as its name suggests, controls all communication. By controlling the clock, the master decides when data is sent and received. Within each clock cycle a full duplex communication is carried out; each side sends and receives one bit of information. Because there is no standard communication protocol, the master can either send data or both send and receive data, depending on the needs of the application. Likewise, the slave can either receive data or both receive and send data back to the master.		The master, as its name suggests, controls all communication. By controlling the clock, the master decides when data is sent and received. Within each clock cycle a full duplex communication is carried out; each side sends and receives one bit of information. Because there is no standard communication protocol, the master can either send data or both send and receive data, depending on the needs of the application. Likewise, the slave can either receive data or both receive and send data back to the master.

	The "Slave Select" line is not required, if only one slave is used. However, using the ~~“Slave Select”~~ line, the master can choose which slave with which to communicate. Note that more than one slave may be selected, simply by applying a logic low to the desired SS lines.		The "Slave Select" line is not required, if only one slave is used. However, using the SS line, the master can choose which slave with which to communicate. Note that more than one slave may be selected, simply by applying a logic low to the desired SS lines.

JamesRein: /* Overview */

2010-02-16T03:07:16Z

Overview

← Older revision		Revision as of 22:07, 15 February 2010
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	The master, as its name suggests, controls all communication. By controlling the clock, the master decides when data is sent and received. Within each clock cycle a full duplex communication is carried out; each side sends and receives one bit of information. Because there is no standard communication protocol, the master can either send data or both send and receive data, depending on the needs of the application. Likewise, the slave can either receive data or both receive and send data back to the master.		The master, as its name suggests, controls all communication. By controlling the clock, the master decides when data is sent and received. Within each clock cycle a full duplex communication is carried out; each side sends and receives one bit of information. Because there is no standard communication protocol, the master can either send data or both send and receive data, depending on the needs of the application. Likewise, the slave can either receive data or both receive and send data back to the master.

	~~Using~~ the “Slave Select” line, the master ~~chooses~~ which slave with which to communicate. Note that more than one slave may be selected, simply by applying a logic low to the desired SS lines~~, as illustrated in the schematic diagram shown above~~. ~~If a given slave is not selected (its SS is high) it disregards signals sent by the master.~~		The "Slave Select" line is not required, if only one slave is used. However, using the “Slave Select” line, the master can choose which slave with which to communicate. Note that more than one slave may be selected, simply by applying a logic low to the desired SS lines.

Thomas Peterson: /* Code */

2010-02-15T05:03:27Z

Code

Show changes

Thomas Peterson: /* Slave Code */

2010-02-11T00:26:00Z

Slave Code

← Older revision		Revision as of 19:26, 10 February 2010
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	* Last Modified: 10-FEB-2010 *		* Last Modified: 10-FEB-2010 *
	****************************************************/		****************************************************/


	#include "HardwareProfile.h"		#include "HardwareProfile.h"
	#include <plib.h>		#include <plib.h>

Thomas Peterson at 00:04, 11 February 2010

2010-02-11T00:04:26Z

Show changes

Thomas Peterson at 22:52, 10 February 2010

2010-02-10T22:52:43Z

← Older revision		Revision as of 17:52, 10 February 2010
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	== Code ==		== Code ==
	[[Image:Pic32_spi.png]]		[[Image:Pic32_spi.png\|\|thumb\|right\|x500px\| PIC32MX SPI Module Block Diagram (click to expand) ]]

	This code, coupled with the circuit diagram above, sends one of two bytes of data from the master to the slave, and back, so the master can output which byte is sent via [[PIC32MX: RS232\|RS232]] communication protocol.		This code, coupled with the circuit diagram above, sends one of two bytes of data from the master to the slave, and back, so the master can output which byte is sent via [[PIC32MX: RS232\|RS232]] communication protocol.

Thomas Peterson: /* Code */ Added block diagram

2010-02-10T22:42:55Z

Code: Added block diagram

← Older revision		Revision as of 17:42, 10 February 2010
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	== Code ==		== Code ==
			[[Image:Pic32_spi.png]]

	This code, coupled with the circuit diagram above, sends one of two bytes of data from the master to the slave, and back, so the master can output which byte is sent via [[PIC32MX: RS232\|RS232]] communication protocol.		This code, coupled with the circuit diagram above, sends one of two bytes of data from the master to the slave, and back, so the master can output which byte is sent via [[PIC32MX: RS232\|RS232]] communication protocol.