iMX.7D LPDDR3 problems

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iMX.7D LPDDR3 problems

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thomaskofoedhan
Contributor III

We have a new board with an combined eMMC + LPDDR3 RAM from Micron which we can't connect to. We can use NXPs DDR Test Tool to download our configuration and then read/write registers in the CPU without problems, but if we try to access the external RAM the processor hangs until we reboot. We can also not measure any DDR clocks or other signals (do not have access to all of them).

Doing the same on the EVM board with the exact same configuration file we can measure a DDR clk, read/write registers, and trying to access external RAM does not make the processor hang. We can off-course not use the RAM because it is the wrong configuration.

It must therefore be a hardware difference that causes this, but what?

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Yuri
NXP Employee
NXP Employee

Hello,

I've sent some comments regarding the schematic. 

Regards,

Yuri.

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thomaskofoedhan
Contributor III

Hello Yuri,

removing the pull-up resistor on the JTAG_MOD pin solved our problem with the LPDDR3 memory access.

I just don't understand why, because in the datasheet (table 4 on page 19) it states that this pin has an internal 100k pull-up resistor. If this is correct then why did it help removing my resistor?

Regards,

Thomas

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Yuri
NXP Employee
NXP Employee

Hello,

  Hardware Development Guide for i.MX 6 recommends to pull down the JTAG_MOD

for normal operation (to avoid unpredictable behavior / entering Boundary Scan mode ) 


<
http://cache.nxp.com/assets/documents/data/en/user-guides/IMX6DQ6SDLHDG.pdf  >

Regards,

Yuri.

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Yuri
NXP Employee
NXP Employee

Hello,

  Please create request and attach schematic with LPDDR3 datasheet

there to analyze it.

Support|NXP 

Regards,

Yuri.

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