Interfacing with a Secure Digital (SD) card - Revision history

Lynch at 07:54, 16 February 2009

2009-02-16T07:54:43Z

Mat Kotowsky at 20:07, 12 February 2009

2009-02-12T20:07:55Z

Mat Kotowsky: /* Application */

2009-02-12T20:04:14Z

Application

Mat Kotowsky: /* Capacity Availability */

2009-02-12T05:58:20Z

Capacity Availability

Mat Kotowsky: /* Operation */

2009-02-12T05:54:11Z

Operation

Mat Kotowsky: /* Operation */

2009-02-12T05:53:20Z

Operation

Mat Kotowsky: /* Operation */

2009-02-12T05:50:26Z

Operation

Mat Kotowsky: /* Application */

2009-02-12T05:13:38Z

Application

Sean Wood: /* Application */

2009-02-12T01:48:14Z

Application

Mat Kotowsky: /* Capacity Availability */

2009-02-12T01:04:42Z

Capacity Availability

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-== Original Assignment ==
-Establish SPI communication between your PIC and a Secure Digital (SD) card for data logging.  Demonstrate the ability to store data on the card and to read it back later.
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 An SD card has 9 pins.  Only 7 of these pins are used to communicate with an SD card in SPI mode.  SD cards require between 2 and 3.6 VDC.  In this lab, we use a bench top power supply to provide 3.3 VDC to both the PIC and to the SD card.  50k pull-up resistors are essential, even for the pins that are not being used for SPI communications.  Note that a pull-up resistor should not be used on the clock line.
-[[Image:SD_Circuit.JPG|center|thumb|400px|Wiring diagram for an SD card (Foust, 2004)]]
+[[Image:SD_Circuit.JPG|center|thumb|400px|Wiring diagram for an SD card [http://www.cs.ucr.edu/~amitra/sdcard/Additional/sdcard_appnote_foust.pdf (Foust, 2004)]]]
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 //// permission.  Derivative programs created using this software    ////
 //// in object code form are not restricted in any way.              ////
+////                                                                 ////
+//// Modifications for ME333 Winter 2009 Lab 5 by                    ////
+////      Colleen Fryer, Sean Wood, and Mat Kotowsky                 ////
+////                                                                 ////
 /////////////////////////////////////////////////////////////////////////

@@ Line 145: / Line 145: @@
 === Capacity Availability ===
-The application allows the user to provide a 2-byte memory address and enter one byte into that address.  That amounts to 64 KB of total memory -- considerably less than the 2 GB of memory the SD card is purported to have.  This is because the example program only reads and writes '''bytes''' of memory from specific '''16-bit''' addresses.  In reality, the SD card stores data not in single bytes but in 512-byte blocks, and the driver assumes a '''32-bit''' address space, not a '''16-bit''' address space.  In order to realize the full capacity of the SD card, one must read and write entire 512-byte buffers and use most of the 32-bit address space.  This allows for total theoretical capacity of 2 TB, though no SD cards of this capacity currently exist (as of early 2009).
+For ultimate simplicity, this application allows the user to provide a 2-byte memory address and enter one byte into that address.  That amounts to 64 KB of total memory -- considerably less than the 2 GB of memory the SD card is purported to have.  This is because the example program only reads and writes '''bytes''' of memory from specific '''16-bit''' addresses.  In reality, the SD card stores data not in single bytes but in 512-byte blocks, and the driver assumes a '''32-bit''' address space, not a '''16-bit''' address space.  In order to realize the full capacity of the SD card, one must read and write entire 512-byte buffers and use most of the 32-bit address space.  This allows for total theoretical capacity of 2 TB, though no SD cards of this capacity currently exist (as of early 2009).
 == References and Further Reading ==

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 [[Image:Operation.jpg|center|thumb|400px|Operation of the card interface program]]
-The user can select whether to read or write by pressing R or W at the prompt.  The user then selects a 16-bit memory address by entering 4 hexadecimal integers.  After 4 integers are typed, the program will display the one byte of data at the given memory location or will prompt the user to enter data, depending on if read or write has been selected.  If write has been selected, the user can enter two hexadecimal integers.  After they are entered, the PIC will write out the value to the SD card at the specified memory location.
+The user can select whether to read or write by pressing R or W at the prompt.  The user then selects a 16-bit memory address by entering 4 hexadecimal integers.  After 4 integers are typed, the program will display the one byte of data at the given memory location or will prompt the user to enter data, depending on if read or write has been selected.  If write has been selected, the user can enter two hexadecimal integers.  After they are entered, the PIC will write out the value to the SD card at the specified memory location.  The user is then returned to the read/write prompt.
 == Future Work ==

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 == Operation ==
-Interacting with the SD card is done via a PC connected by RS-232 to the PIC.  Any terminal emulator can be used to connect to the correct COM port at 19200 baud.  Once connected, powering up or resetting the system will cause the PIC to communicate with a card.  If it cannot, the program will report an error message and quit.  If it is successful in initializing communication with the card, it will immediately print the contents of the SD card's identification register, then prompt the user to read or write to a given memory address.
+Interacting with the SD card is done via a PC connected by RS-232 to the PIC.  Any terminal emulator can be used to connect to the correct COM port at 19200 baud.  Once connected, powering up or resetting the system will cause the PIC to communicate with a card.  If there is an error and the PIC can't connect, the program will report an error message and quit.  If it is successful in initializing communication with the card, it will immediately print the contents of the SD card's identification register, then prompt the user to read or write to a given memory address.
 [[Image:Operation.jpg|center|thumb|400px|Operation of the card interface program]]

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 === Application ===
-The original, unmodified application code was included in the newer version of CCS mentioned above.  Note that as of Winter Quarter 2009, these drivers are not available in the Mechatronics lab but are available on the installation media provided in our lab kits.  Modifications were made to the code to change the assignment of the SPI pins, modify the includes to use our PIC, and properly configure RS232 and the main clock.  Additional modification was made to make the application display the contents of the SD card identification register.  All modifications contain "MODIFIED" in their comments.
+The original, unmodified application code was included in the newer version of CCS mentioned above.  Note that as of Winter Quarter 2009, these drivers are not available in the Mechatronics lab but are available on the installation media provided in our lab kits.  Modifications were made to the code to change the assignment of the SPI pins, tailor the preprocessor directives to use our PIC, properly configure RS232 and set the main clock frequency.  Additional modification was made to make the application display the contents of the SD card identification register on startup.  All modifications contain "MODIFIED" in their comments.
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