SDHC卡SPI初始化
我正在开发一个目前仅支持 SDSC v1 卡的嵌入式系统。由于找到小于 2 GB 的卡变得越来越困难，我正在尝试添加对 SDHC 卡的支持。与卡的通信是通过 SPI 总线完成的。
所以这就是我初始化卡的方法：
- 发送 CMD0。卡返回0x1
- 发送CMD8 + 0x1AA。卡返回 0x1 和 0x1AA
- 发送 ACMD41。卡返回 0x0。
后来我看了MBR，发现在0x30处有一个FAT16分区LBA。但是，从该地址 (0x30*512) 读取扇区会返回 0x01 0x09 的重复...
- 发送 ACMD41 时，我发送命令 id 0x69。正确吗？或者我应该先发送 CMD55，然后发送 CMD1？
- 图表 1 显示我需要在发送 ACMD41 后发送 CMD58，可能还需要发送 CMD16。有必要吗？我无需执行这些操作就能够读取有效的 MBR。
I'm working on an embedded system that currently only supports SDSC v1 cards. As it's getting harder and harder to find cards less than 2 GB, I'm trying to add support for SDHC cards. The communication with the card is done via the SPI bus.
So here is what I'm doing to initialise the card:
- Send CMD0. Card returns 0x1
- Send CMD8 + 0x1AA. Card returns 0x1 and 0x1AA
- Send ACMD41. Card returns 0x0.
Afterwards, I read the MBR and figured out that there is a FAT16 partition at 0x30 LBA. However, reading a sector from that address (0x30*512) returns a repetition of 0x01 0x09...
- When sending ACMD41, I'm sending command id 0x69. Is it correct? Or should I send CMD55 and then CMD1?
- A diagram 1 shows that I need to send CMD58 and possibly CMD16 after sending ACMD41. Is it necessary? I was able to read a valid MBR without doing them.
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“ACMD”命令都需要 CMD55 后跟相关命令。
例如，对于命令 ACMD41：
不要忘记将 0b01000000 与第一个参数进行 OR 运算。实际命令不是 55，而是
55|0b01000000（0b01110111，十进制119）。我在 SD_command 函数本身中执行此操作。连接 SD 卡是一件非常痛苦的事情，所以不要放弃。祝你好运！
"ACMD" commands all require a CMD55 followed by the relevant command.
For example, for command ACMD41:
Don't forget to OR in 0b01000000 to the first argument. The actual command isn't 55, it's
55|0b01000000(0b01110111, decimal119). I do it in the SD_command function itself.Interfacing to SD cards is a HUUUUUGE pain, so don't give up. Good luck!