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SparqEE Forum • Problem with TTL/UART port
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Problem with TTL/UART port

Posted: Sun Oct 30, 2016 1:22 pm
by Islandboi
Hi all,
New to this forum so hope I don't ask too many stupid questions!.

I am having problems using the modem via the UART interface. I am using my
own carrier card which follows the general guidelines for UART operation
set out in your guidelines. Same problem appears on both modems I have.

Using the USB port on the modem I can get responses, set bit rate to 9600
and save it, and get information re carrier, signal level etc.

However I am unable to communicate with the module using the UART
connections. Using a Freetronics usb to UART converter which works well on
other projects. I need to use 9600 as connection speed which I have set
and using AT+ZBITRATE=? returns 9600 using the USB port but no response
from UART port.

Checking with oscilloscope on RX pin of module shows activity on this pin
when sending commands via the USB adaptor to UART connection. Seems to
me that I need to switch from USB to UART operation but cannot see how this
is done.?

The information I have shows V-BUS connected to VIN, but should this be
there when using UART only ?.

Any assistance would be welcome.

The application I want to use these modems in uses a PIC32MX150 processor
programmed with MMBasic, which is a really simple system to get running.
See http://micromite.org/micromites/ in fact rather easier than
Arduino and RP.

Have used it with 2G modems a lot, but because the Telco here (Australian
Telstra ) is shutting down 2G services 1st December need to get 3G modems
in the systems which are used for remote telemetry.

Re: Problem with TTL/UART port

Posted: Sun Oct 30, 2016 6:16 pm
by donjohnii
So it sounds like you're communicating with it over the modem, which means it's on.

UART wise, your VREF needs to be whatever Voltage you're using on the USB-UART converter... if it's 5V put 5V to VREF, if you're using 3.3V put 3.3V to VREF. VIN only needs VBUS if you're powering the CELLv1.0 using the USB which it sounds like you're using so yes, jumper VBUS to VIN - but if you've got it working already, it means it's powered up.

I would just make sure you've got your GND connected, VREF correct, then change the polarity of TX/RX and make sure that's correct.