imx6q, DTE DCE question

[angelo_d]

Dear all,

in all the documentations i find in the network, and as well  in HCI_UART specification, a DTE is

the HOST of the communication, so it SETS the RTS and check CTS.

Because of the initial nature of the RS232, DTE -> DCE connection  that was using a straight connection,

the DTE TX(Output) must still be DCE TX(that must be Input at this DCE "connector" side, and i suppose

swapped inside the device to match UART chip RX).

So, from the above assumptions, i can't understand the image below (imx6 dual / quad reference

manual, page 5163):

In DCE, TX should be an input, as well as RTS. In DTE, TX is an output, and of course RTS also.

The manual shows TX as output in DCE. This seems at my humble opinion, wrong.

What am i missing here ?

Regards

Angelo

[igorpadykov]

Hi Angelo

understanding of RM is correct, also signal directions are given in

Table 90. UART I/O Configuration vs. Mode  i.MX6DQ Datasheet (rev.4, 7/2015).

Actually on this table UARTx_RX_DATA = Output Serial data from DTE to DCE

acts as "TX" - an output, as well as RTS which complies with your understanding

of DTE -> DCE connection.

Best regards

igor

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[angelo_d]

Hi Igor,

many thanks for the support, sorry but still see some understanding issues:

1) on rev.4, 7/2015, just to be aligned, the table seems 81 (90 was in the old verison).

2) Still the table aligns to the user manual, and shows TX as output in DCE and as input in DTE.

What i miss here ? I can be completely wrong, but as far as i know,

DCE devices have the TX pin as an input, and related internal IC in the modem devices shows DATA_TX pin as input pin.

3) Another possible issue to me is that in both In DTE and DCE columns, i see description is the same as "serial data from DCE to DTE", while i am expecting on both "serial data from DTE to DCE", since DTE is always

the transmitter in TX. It is like freescale is considering an inverse sense of the signals.

Can you help me to understand ?

[igorpadykov]

Hi Angelo,

below DTE mode: transmitter is TX ("Output Serial data from DTE to DCE").

The same, RTS is also output.

~igor

[angelo_d]

Hi  igorpadykov    

thanks,

sorry, i was reading the "industrial" datasheet, now we are aligned on Table 90.

Sorry, but still for me is not clear.

You are showing here above "Output" "Serial data from DTE to DCE" on the UART_RX line.

While RTS as output is ok in DTE mode, i am expecting TX to be an output in DTE mode too.

This is from the RS232 basics i had, you see, DTE is the host that transmit, and control RTS.

Regards

angelo

[igorpadykov · Accepted solution]

' "Output" "Serial data from DTE to DCE" on the UART_RX line '-

you can ignore abbreviation "RX", really it is transmitting line,

outputting data.

[angelo_d]

Hi Igor,

many thanks,

good to know,

after some additional study i re-edit this reply.

Some other users claimed out also this TX RX inversion.

As pointed out also here:

IMX6q UART5 Bluetooth connectionWeisong Liu

Weisong Liu     21-apr-2014 2.30 

And here

i.MX6 UART connection.

Satoshi Shimoda     17-lug-2014 22.07  (in risposta a Tao Zheng)

David Wood     23-gen-2015 15.08

What i understand is that documentation reflect what hardware really do.

And is more an hardware conceptual error, since the internal UART is designed from freescale as a mix of DCE and DTE.

Since TX is an output, as is in general DTE and UART 16650 chip,

whle RTS is an input, as in DCE ic's, and in fact it is an output in 16650 chips.

Best Regards

Angelo Durgehello