TRAXMOD

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TRAXMOD is a small digital audio player using the Microchip PIC32MX340F512H high speed microcontroller chip (previous versions used NXP LPC2103 ARM7TDMI microcontrollers). Currently, TRAXMOD can play raw wave audio streaming off of a FAT formatted MMC/SD Card at 44100Hz, 16 bits, stereo.

Finding a microcontroller chip that can do back-to-back SPI data transfers correctly and at high speeds hasn't been easy. Previously, our breadboarded LPC2103 player could only get up to about 17MHz before reading data from our SD Cards started producing incorrect data. Maybe that's because of our use a breadboarded circuit, or maybe its because of LPC2103 errata, we don't really know for sure.

When we started using the PIC32MX340F512H, we wanted to see just how fast we could clock the SPI port and still be able to read correct data from the SD Card. What we found was that some SD cards could be clocked even faster than the 25MHz SD Card specification and the PIC32 could still read data correctly enough to play some raw wave audio off of them. At this point, it seems apparent that maximum speed is dictated by the SD Card used, not by our circuit or the microcontroller chip being used.

Worked at 30.1056MHz
32MB	Kingston	Japan
128MB	Kingston	Taiwan
1GB	Kingmax Platinum 50X (not 100% good)	Unknown
2GB	Toshiba (not 100% good)	Japan
Worked at 28.224MHz
256MB	SanDisk	China
1GB	Crucial (Micro SD)	Taiwan
1GB	Lexar	Korea
2GB	Dane-Elec	Japan
2GB	Kingston Patriotic Multipack	Korea
2GB	A-Data 150X Turbo	Unknown
Failed at 28.224MHz
1GB	Kingston 50X Elite Pro	Taiwan
4GB	A-Data SDHC Class 6 Turbo	Unknown

Interestingly, the A-Data SDHC Class 6 card could not even get past 28.224MHz. Supposedly, the SDHC specification allows up to 50MHz clock rates, twice the 25MHz SD Card specification. However, from this card, it appears that just being labeled SDHC isn't enough to tell you that the card will be able to be clocked any higher than it's SD Card brethren. Doh!