- Radio RF Electronics
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PIC - MMC (Multi Media Card) Flash Memory Extension
It is easy to interface a MMC (MultiMediaCard) with a MicroChip PIC via the SPI (Serial Port Interface).
This is a very handy data logging circuit with lots of memory for data storage.
I2C RAM's or EEPROM's are hardly available at sizes bigger than 256kb, but this solution with a 64MB Flash MMC is not
to beat in both cost effectiveness and storage volume!
Also see: Atmel ATmega - MMC (Multi Media Card) Flash Memory Extension.
Hardware:
This version utilizes a PIC16F876, but it's easy to port the schematic and software to other PIC's.
The MMC is connected to the SPI pins of the PIC via simple resistor voltage dividers to transform the +5V high
levels to about 3.3V used by the MMC. The supply voltage for the MMC (2.7V - 3.6V) comes from a LD1086V33 voltage regulator (3.3V)
or equivalent. It is possible to run the PIC at 3.3V, but then the AD converters are not as stable as at 5V.
The data-out pin from the MMC goes directly to the PIC, because 3.3V is high for the PIC anyway.
Software:
BUGFIX 30-NOV-2004: Added serialterminate() to mmc.c for reliable termination of the sent string over the serial port.
UPDATE 02-DEC-2004: Version 2 of serterm (serterm2) released
UPDATE 05-NOV-2005: The ser example got it's own page
UPDATE 09-DEC-2005: Check the Atmel-MMC page for an update of the MMC code (regarding the while-loop)
Compile the PIC program's with the CC5X compiler (free version available - runs on Linux with "dosemu")
mmc.c:
This C-prg. writes ASCII characters into the RAM of the PIC. Then the content of the RAM is written to the MMC.
In order to verify the successful data transmission to the MMC, 512 bytes are read back and sent directly to the Linux box
via the serial port (RS232) and are displayed by "serterm".
Furthermore the PIC returns any character received (via interrupt service routine) via the serial port back to the Linux machine.
Use "ser" to send 3 characters and receive them.
sercom.c:
This example only sends back any character received by the PIC (via interrupt service routine)
via the serial port. Use "ser" to send 3 characters and receive them.
serterm2:
Linux software to receive serial data from the MMC example. NOTE: It uses ttyS1
Another way for reading the serial port on Linux is this very handy bash script :
#!/bin/bash
while true
do
read LINE < /dev/ttyS0
echo $LINE
done
Third way for reading the serial port is the Debian
Packge "ttylog":
# ttylog -b 9600 -d /dev/ttyS0
ser:
Linux program to send characters to the PIC and print out the returned characters. NOTE: It uses ttyS0
Writing to the MMC can be at any speed (i.e. 1byte per hour), but the "sector" is only saved if 512bytes were transmitted.
Software SPI-Interface
Not all PIC's have a SPI-Interface or if you want to use the I2C bus, you'll have to use other pins for the
communication with the MMC. Michael Dworkin has written a very handy sub routine, which will replace the
function char SPI(char d) in the mmc.c example.
You can choose any free port pins for use as SPI interface.
#pragma bit CS @ PORTC.2 // output for chip select CS
#pragma bit SCK @ PORTC.3 // clock output
#pragma bit SDO @ PORTC.5 // data output (PIC)
#pragma bit SDI @ PORTC.4 // data input (PIC)
Don't forget to set the TRIS register!
TRISC=0b.1101.0011; // SCK rc3-0, SDO rc5-0, CS rc2-0
The new SPI function:
char SPI(char out) // software SPI function at about 620 kHz for a 20MHZ crystal
{
char in,i;
for (i = 0; i < 8; i++)
{
nop2();
SCK = 0; // falling edge of clock
nop();
SDO = out.7; // prepare data
nop();
out = out<<1; // shift output byte for next loop
nop2();
in = in<<1; // shift input data for next loop
SCK = 1; // rising edge of clock
nop();
in.0 = SDI; // read input data
}
return in;
}
Credit: Thanks to Michael Dworkin for his MMC tutorial.
Last-Modified: Fri, 09 Dec 2005 17:28:54 GMT
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