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Altera_Forum
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12 years ago

Altera CycloneV SOC Dev board Bootsel defaults

In the 13.0 version of the Cyclone V SOC dev kit (Rev C) the BootSel default is set to 4 which (according to various tables etc) should be a 1.8V uSD card. This seem odd as the uSD socket power I ...
Altera_Forum's avatar
Altera_Forum
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12 years ago

From what I understand is that all SDCards uses the 3.3V interface at startup. Then a configuration(ACMD41/CMD11) is needed to turn the interface to 1.8V. This is only the voltage used on the data&control lines, the power supply should always be 3.3V (2.7V - 3.6V)

You can read a summary on wikipedia : http://en.wikipedia.org/wiki/sdcard there is a topic "electrical interface".

or the complete story in https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf page 15

The SD/MMC controller of the SOC of the Cyclone V can work in 4 modes. DS/HS and requires an interface of 3.3V and SDR12/SDR25 that requires 1.8V.

The speed is however the same, maximum 25MBps. This will thus probably depends if you are using/supporting the "old" SD cards or only the SDHC/SDXC.

I did not find what will happen when you connect an old SD to a cyclone configured to 1.8V