I've been trying to do an SD card interface with the LPC1766 SPI peripheral for a while and right now I'm stuck in a problem that I couldn't find the answer anywhere.
The problem is: SDHC cards are not responding to write and read commands as expected.
Everything works fine on the initialization that was based on Chan's flowchart and on an NXP application note. I can differentiate the cards versions, read the OCR, CID, CSD and determine their sizes.
After that step I start writing single blocks every one second and reading it back to check the data integrity. On a Kingston SDHC 4 GB Class 4 card I can send a first write command but on the second one the card does not even answer (0x00 or 0x01) to the CMD24. With a SanDisk 4 GB Class 4 card the results are different, every command is answered by the card, but I get only zeroes when reading the data back (I'm sure I'm not writing zeroes). If I use SDSC cards, everything works fine.
I'm aware that SDHC are block addressed and not byte addressed and that I need to send ACMD41 with the CCS on for SDHC. I also know that the clock frequency is not an issue (using 400 KHz to start and then 20 MHz to write/read), because I just turned on the CRC checking and all cards are accepting the commands and data. If I stop calculating the CRC all cards reject commands and data.
How do you connect your SD card? Depending on the mode/state the SD(HC) card needs an external pull-up resistor. Without that you read zero, so that may be your problem.