Quectel BC66 Uart Port Baudrate problem

[PepeTheFrog]

Hi,

I have bought a Olimex BC66 Dev Kit some time ago.
The communication is working when using QCom software.
But when we connect to a USB-To-UART converter ( to simulate MCU connection), open a serial terminal and reset the module, this is the result:

Code Select Expand

pá␁␂b°uild° tim°e: 2°019/°12/1°2 20°:45:°37 G°MT +°08:0ð0 °em b°oot:° bac°k fr°om l°ong °pres°s sh°utdo°wn o°r sy°s_reðset␄°
Õ°␈␌␁Óð␁Ù␁°µ␃Ô°¯␃,"␐ða'␐␅pÖž␈%ª}ß,p␎á␅T␐°˜ž"␐ð‡' ␅pÜ␏␁ýÔ°"␃pb
We tried sending the AT commands multiple times with no avail.

[LubOlimex]

Well it seems to make some sense the messages just with some glitches...

Do you have GND line connected? What is the baud rate? Did you try with something like 115200?

[PepeTheFrog]

Yes, GND is connected and the baudrate is 115200.

[LubOlimex]

- What happens when you use the micro USB port of the NB-IoT-DevKit directly? It should also create COM port since the board has built-in converter and if you open terminal you can send AT commands.

- Where is your adapter exactly connected (which pins do you use)? There are at least 3 different RX and TX pins at the headers (You need to use RxD, TxD at EXT4; and not RxD-DBG, TxD-DBG nor TxD-AUX, RxD-AUX).

- How do you power the board when testing the USB-serial adapter?

Some of the signals at these pins are at 1.8V, hence why the schematic under the headers says "!!!Attention!!!Levels!!!".

[PepeTheFrog]

1) It creates COM port to which we can comminicate using QCOM, sending AT Commands.

2) We are using Pin 17, 18 (TX and RX) not DBG or AUX.

3) Power supply is delivered by microUSB connected to PC, not external battery.

[LubOlimex]

I am not sure if the design of NB-IoT-DevKit allows for such usage.

What is the revision of the board so I can test it myself. Is it revision C?

[PepeTheFrog]

No, it is revision D.

[LubOlimex]

Our tests don't show such glitches. We did two tests - one with regular USB and another with USB without data lines (in case the data lines put the built-in CH340T in state that might bug the RX and TX of the external serial-USB converter).

If you power from the USB with data lines you need to ensure that there is no activity on the USB (aka don't open terminal on the COM port created by the built-in CH340T).

If the problem remains try with another USB serial adapter and make sure all connections are solid (a bad ground might cause glitches). The GND pin is #3 of the header.

If nothing seems to solve it there might be hardware issue with the module you have.

Overall it doesn't make a lot of sense to use external serial USB adapter with NB-IoT-DevKit when there is built-in one.

[LubOlimex]

This is our setup testing with external power supply. Using one of the Li-Po battery connector contacts for second GND:

https://imgur.com/Iq1rODx

[PepeTheFrog]

We will try with external battery supply.


For power supply connection which pins have you used?

[LubOlimex]

Pin #1 of EXT1 header is +5V. Any GND pin that you can find. We used the GND pin of the Li-Po connector but you can also split the GND used for the UART cable (thing is there is only one GND pin available on the EXT headers and you need two GND pins - one for power, one for serial cable; might need to improvise).

Another important part is that you need to connect the TX of your cable to the TX of the board, and RX of cable to RX of the board.

[PepeTheFrog]

Another important part is that you need to connect the TX of your cable to the TX of the board, and RX of cable to RX of the board.

This is the problem right here.
We found on the documentation of the BC66 (Hardware design V 1.3 page 30) that the TX had to be connected to RX and viceversa (DCE --> DTE).

By connecting RX to RX and TX to TX everything works.

Could be a documentation error?

[LubOlimex]

No, this is not a documentation error in BC66 documentation, it is just how we designed the board. You are not accessing the BC66 directly anyway. There are voltage translators (since BC66 works at 1.8V and your cable works at 3.3V), also there is BC340 built in converter on the same pins. It is our design choice to already connect RX to TX and TX to RX and lead them out that way. But probably I should mentioned it in the FAQ section since I see how it can be perplexing without checking the schematic.

If you inspect the schematic the connection RX - TX and TX - RX happens near the "Voltage-Level Translators" part.