i.MX8M Mini USDHC3 eMMC IO Voltage

[omar_wolfe-huss]

Hi,

I've been reading through the documentation for the i.MX8M Mini boot from eMMC and have some queries about the IO voltage selection. 

Firstly, Table 6-19 of the reference manual states that BOOT_CFG[1] and BOOT_CFG[0] are used to set the IO voltage for USDHC1 and 2 respectively, which I assume corresponds to USDHC ports 1 and 2. However in the Fusemap (Table 6-43) it states that they control the USDHC IO Voltage for Normal Boot Mode and Manufacturer Mode. These seem like different things, unless Normal Boot Mode only uses port 1 and Manufacturer Mode uses port 2? If they are not associated in that way then which of the tables is correct?

Additionally Table 6-19 states that the IO voltage for USDHC3 is set through a fuse that isn't attached to a GPIO, and that it defaults to 3V3. Is there a way to make USDHC3 run at 1V8 before boot, in the case of booting from an eMMC card at 1V8 IO on port 3. The schematics for the dev board show that a 1V8 eMMC card is attached to port 3 and that to get around this restriction the USDHC3 supply is simply tied to 1V8 - is this the recommended solution to the problem? If that is the solution then what is the purpose of having the fuse for the IO voltage selection?

Thanks

[weidong_sun · Accepted solution]

Hi Omar,

    ROM code in i.MX8M MINI doesn't care these 2 bits BOOT_CFG[1] & BOOT_CFG[0] , It means these 2 bit don't affect booting board.

    For example, the IO VOLTAGE of USDH3 port on i.MX8M MINI EVK is determined by "NVCC_NAND",

eMMC IO voltage matching:

so if you want to use eMMC or SD with 3.3V IO, use 3.3V for NVCC_NAND, please!

So about boot configuration selection on BOOT_CFG[1] pin,  refer to the way of i.MX8M MINI EVK design files, please!

Have a nice day!

BR,

Weidong

[omar_wolfe-huss]

Hi weidong.sunthanks for the information. If the ROM doesn't look at those two bits then what are they used for?

We'll be designing the interface as done in the EVK design file, so with a 1V8 IO voltage.

Thanks

[weidong_sun]

OK, Omar,

   you can USE the same circuits for  BOOT_CFG[1] & BOOT_CFG[0] AS that of i.MX8M MINI EVK. Or refer to my suggestions:

1. IO voltage for USDHC1/2/3

From the list, NVCC_SD1/2/NVCC_NAND can be supplied 0~3.8V, you can use different power for each of them respectively, for example, 1.8V for NVCC_SD1 , 3.3V for NVCC_SD2, 1.8V for NVCC_NAND, or 1.8V for all of them. If you use 3.3V IO, you must pay attention to the comment on schematic( disable internal pull up/down, and use external pull up/down).

2. BOOT_CFG[1]

Handle this pin like this:

Here DNP means "Do Not Place", After your design is done, you can do a test with populating or removing R76, you will find that system booting can't be affected.

As for BOOT_CFG[0], don't need to handle it, use default, please!

Have a nice day!

BR,

Weidong