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i.MX 6Solo(UART DTE/DCE mode, hardware bug?)

Question asked by Ilya Byckevich on Jan 28, 2020
Latest reply on Jan 31, 2020 by Ilya Byckevich

Hi, I use  MCIMX6S6AVM08AC chip with Linux(imx_4.1.15_2.0.0_ga) and I try to use UART with flow control.

Issue 1:

It works, but RTS and CTS signals are inverted!(uart_work.png)

On schematic(DEV_* - pins from LBEE5KL1DX):

D25(ALT2 = UART3_CTS_B) connect to DEV_CTS

F23(ALT2 = UART3_RTS_B) connect to DEV_RTS


# Test devmem2 utility(read USB_nID reg)

$ devmem2 0x2184000


# Read UART3_UFCR reg

$ devmem2 0x21EC090


As you can see DCEDTE-bit is 0, but the signal from D25 is still like RTS.

Issue 2:

I have another device where the connection was changed(in the correct way):

On schematic(DEV_* - pins from LBEE5KL1DX):

D25(ALT2 = UART3_CTS_B) connect to DEV_RTS (direction <- ONLY from rts to cts)

F23(ALT2 = UART3_RTS_B) connect to DEV_CTS (direction -> ONLY from rts to cts)

Now it doesn't work, because between iMX and LBEE5KL1DX I used SN74AVC4T245 and data transmission allowed only

in the above direction. The "fsl,imx21-uart" driver have the "fsl,dte-mode" option. I checked this feature and signals swapped but Tx doesn't work.(uart_don't_work.png)

       If I physically rewired signals from iMX (UART3_CTS_B and UART3_RTS_B) it works.


Can I swap cts and rts signals on iMX without board damaging?