SDIO interface voltage levels

IoT Modules
1

I want to provide a SD card interface to WP7607, and I’m looking at the mangoh red board schematic as a baseline. But I can’t really work out the voltage levels…

It’s my understanding that SD cards operate at either 1.7-1.95v or 2.7-3.6v

I can’t really see the relevance of the 2.85v in the WP Tech Spec? It seems very precise but doesn’t seem to relate to anything. On top of that the Mangoh board uses a SD supply of 2.95v which again is precise but I can’t see the reason why.

Could somebody please enlighten me?

Thanks

2

do you mean you want to turn down the output of module SDIO pin to be 1.8V?

3

Hi. No I wanted to know the significance of the 2.85v value, and why the Mangoh board is using 2.95v (as opposed to 3.0 or 3.3v)

4

sorry, no idea, but i found that it still works for 3V SD card system.

5

Hi,

I want to turn down the output of module SDIO pin to be 1.8V on WP7607
How to turn down the output of module SDIO pin to be 1.8V?

6

Are you using SDIO for SD card?

I saw the folowing in yocto source which seems can set the voltage, you can give a try:

/kernel/driver/mmc/core/core.c, in function mmc_power_up(),

mmc_set_ios(host);
/* Try to set signal voltage to 3.3V but fall back to 1.8v or 1.2v */
// if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_330) == 0)
// dev_dbg(mmc_dev(host), “Initial signal voltage of 3.3v\n”);
// else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180) == 0)
if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180) == 0)
dev_dbg(mmc_dev(host), “Initial signal voltage of 1.8v\n”);
else if (__mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_120) == 0)
dev_dbg(mmc_dev(host), “Initial signal voltage of 1.2v\n”);