I cannot read data from sci-tx port(Serial communication)

Part Number: TMS320F280025C

Other Parts Discussed in Thread: LAUNCHXL-F280025C, C2000WARE

I have a simulink model for a power electronics project and i want to see detailed data using SCI-TX port in simulink. For this, i have created 2 codes, one is for code generation and the other one is for watching the data. Both of the codes work without a problem in LAUNCHXL-F280025C. The default pins are GPIO28 and GPIO29 for TX and RX, and when i want to change these pins, using the hardware switch at the launchpad also creates no problem and i am able to also use GPIO16 and GPIO17 pins. Hovewer, using the TMS320F280025CPNSR (this processor is used in my project card), i cannot get the data interface to work in any ways. The pins are selected as GPIO16 and GPIO17 in project card. In summary, with the launchpad, i am able to see the data on sci pins, but the same codes do not work for the control card (i change the build configurations to TI F28002x.) I have tried lots of methods, i tried GPIO2 and GPIO3 pins instead, didnt work. I even tried to change the value for OUTPUTXBAR7 to SCI-TX(6) but this didnt work either. Even this simple code where i read adc values and send it to serial pin does not send any data to my SCI-TX pin.(The codes themselves work but i do not see any data in model.) The only difference is that the FTDI we use is XDS100, but i have seen this card being used without any problem in other projects ( for example 49c.) The pins do not have a physical connection problem, as we tested them with a multimeter. I ran the sample sci code and my normal code on controlcard. The signals without noise came from controlcard, and i was able to see these signals using the TX pin on hardware.(GPIO16) Hovewer, it seems that the data is not being sent to pc, as i was not able to see any data in my interface model and putty application. The signal with noise comes from launchpad, but i am able to correctly read the data from my interface model. I dont have any ideas left, any suggestions?

[Bhanu Prakash]

Hi Hasret,

Found a similar issue in an MATLAB Answer which could probably give you more insights on the issue:

https://www.mathworks.com/matlabcentral/answers/2098741-sci-tx-doesnt-work-properly

Answer 1

[Mukul Choudhury]

Hi Hasret,

Your description points at a routing problem on the controlCARD, not a code problem — the SCI peripheral is clearly working since you see traffic on GPIO16 with a scope. Here are the most likely culprits, in order:

1. controlCARD FTDI is wired to GPIO28/29, not GPIO16/17 (most likely)

The LAUNCHXL-F280025C has a physical switch that swaps the XDS100 UART bridge between GPIO28/29 and GPIO16/17. The TMDSCNCD280025C controlCARD does not have that swap — its onboard XDS100 UART lines are hard-wired to the SCI-A default pins (GPIO28/29 on the F280025C pinout brought out to the DIMM edge). So when you move the Simulink SCI to GPIO16/17, the signal comes out on that pin (which is why your multimeter/scope sees it), but it never reaches the FTDI, and nothing arrives at PuTTY.

Fix: In your Simulink Hardware Board settings, set the SCI-A pins back to GPIO28 (TX) / GPIO29 (RX) for the controlCARD build. If your project card breaks GPIO28/29 out to a header, that's the path to use; if it doesn't, you'll need to physically wire from the DIMM's GPIO16/17 to the controlCARD's XDS100 UART pins on the docking station.

2. controlCARD isolation / UART enable switch

The TMDSCNCD280025C docking station has switches/jumpers to enable the isolated UART path to the XDS100. Check the docking station user guide (SPRUIV6 or similar) — one of the DIP switches typically enables the UART-to-USB bridge. If it's off, GPIO28/29 traffic is generated but blocked before the FTDI.

S1:A Position 1: JTAG ENable- this should be on which connects the XDS100v2 emulation logic and the MCU

S1:A Position 2: ISO UART communication enable - this should be on - The C2000 MCU’s GPIO-28 (and pin 76 of the 180-pin controlCARD connector) will be coupled to the FTDI’s USB-to-Serial adapter

3. Clock source mismatch → wrong baud rate

Check for the clock source. If internal clock source does not work, try with the external clock.

Check: In Configuration parameters -> Hardware Implementation → Target hardware resources -> Clocking, confirm the oscillator selection matches the controlCARD (external XTAL). Also verify the bit-time on your scope against 1/baud.

Diagnostic order

1. Move SCI back to GPIO28/29, rebuild, and try PuTTY on the controlCARD — this alone likely solves it.

2. If still silent, scope GPIO28 during a transmit — is the signal there?

3. If yes, check the dock's UART-enable switch.

4. If baud looks wrong, fix clock config.

Hope this helps.

Thanks,

Mukul