Hi Jianxin,
You can see the schematic of SCM-i.MX6Q, if you do not use the JTAG you can not float all of them.
You need to do the following actions before float them. Then you can connect them separately to test mode.
PU(10K)
JTAG_TMS
JTAG_TDI
Pull UP JTAG_nTRST to high votage
PD(4.7K)
JTAG_MOD
JTAG_TCK and JTAG_TDO can directly floating.
Have a great day,
Rita
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