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TMS570LC43x using SCI but maybe need to set RTS / CTS. How?

Markus Auer
Intellectual 420 points

Other Parts Discussed in Thread: HALCOGEN

Hey guys,

I am using the TMS570LC43x MCU of TI and i am using the SCI3 Pins to communicate with.
The aim is to send at commands to a Telit LTE module over this interface.

i checked each connection (mcu-pc and lte-pc) with a terminal program hTerm. Everything works so far if i just take one device alone. Sidenote if i want to communicate from hTerm with the LTE module i need to turn on "RTS".

So when i connect the mcu to a ttl-rs232 converter-rs232 cable- to the LTE module it doesnt work. (i want to press a button, send an at command, and with the answer i want to turn on a led on the mcu).


Since i am not that good with the uart interface, i think one reason could be that i am not using RTS/CTS from MCU to the converter so the LTE module needs it (maybe!!).

I looked in this forum but i couldn't find how to connect or use RTS/CTS exactly with this MCU.

I need really help by this guys.if you have any further questions dont hesitate to ask!

Hope for any hints!

Kind regards,

Markus

  • 0
    TI__Guru**** 191886 points
    Hi Markus,
    The UART in Hercules family does not support RTS/CTS flow control.
  • 0 in reply to Charles Tsai
    TI__Guru 69070 points

    If your other device does use the RTS/CTS lines though there are a couple options.

    1) use GPIO in conjunction w. the UART to implement RTS/CTS.

    2) create a cable with the correct loopback so that it's automatic.  In this case you're basically bypassing the handshake though so it would be what you would do if the other module is using the RTS/CTS but doesn't really need flow control..  it may just 'respect' flow control of the other device.

    You might want to get a good book that covers serial ports ...

    I used to love the serial port chapter in

    but there may be others that are good too..

  • 0 in reply to Anthony F. Seely
    Intellectual 420 points
    Thx for the answer Anthony.

    First i try to disable flow control on the LTE module.

    But anyway i am interested in the way from your number 1. Can you explain how i can set this up exactly. I am using Pin 3 and 4 for the SCI RX and TX on J1 and PIN 1 and 2 for +5V and GND on J3. Let's assume that we take on J1 the Pin 5 (GIOA_7) for RTS and PIN 8 (GIOA_6) for CTS. What do i have to do and configure (in halcogen and ccs). Please as detailed as you can.

    Where do you mean the loopback? is it only on the mcu side or only on the LTE module side or a cable from mcu to LTE?

    And the (gray) book you are recommend seems to be pretty old from 1989. Is it still worth to buy? Because the newer one cost 72 euros so quite expensive for a student :). Or is there another good book you can recommend?

    Thanks in advance for the hints !

    best regards,

    Markus
  • 0 in reply to Markus Auer
    TI__Guru 69070 points
    Markus,

    So the wikipedia on RS-232 is pretty good too.. en.wikipedia.org/.../RS-232
    The first thing you need to do is figure out which your LTE module is .. the DTE or DCE.
    Then you need to make your software behave like the other 'side' of the conversation.
    That will tell you which signal you are listening on and which you are driving.

    Then you just can use the signal you are driving in GPIO output mode and the signal you are listening on in GPIO input mode with an interrupt. In the interrupt service routine you can catch all the state changes and use these to throttle whether or not you allow your UART to transmit or whether it needs to pause. Likewise you could possibly throttle the LTE from sending you data if you need more time to process it locally.

    But this is all a software issue at a higher level than the UART as Charles mentions the UART doesn't have a buffer and doesn't manage these pins in hardware.

    Most of the time if your UART processing on receive is fast enough and transmit is slow enough you can just let the other side of the cable receive it's own signals (with a loopback) and comms will work. There was a nice picture of various types of cables for this in the Silver book. I'm a little older ;) and never bought the golden book but the silver was required reading in my college and I wore it pretty thin. Then I gave it to a good friend ..

    Best Regards,
    Anthony