Hi,
I am attempting to connect an Arduino MKR1000 via UART to a SparqEE Cell 1.0 3G GSM module. Once a connection is established, all is fine, but the initial startup of the serial communication seems to be a bigger issue.
I am running the UART on 38400 baud. On the arduino side a "Serial2.begin(38400)" does the job, the Cell was configured once with "AT+ZBITRATE=38400;AT+ZBITRATE=S". As I wrote, the configuration seems to be correct as I can communicate as soon as the startup succeeded. Both sides are talking 8N1.
I have two devices with both a MKR1000 and a Cell, both devices are behaving identically. The Cell modules on powerup successfully will open up a stable 3G connection to my GSM provider.
The problem is, that any attempt to communicate on 38400 baud will fail after a system powerdown/powerup. Regardless how long I wait, no reaction is to be seen from the Cell via UART.
A strange workaround manages to kick off the communication: if I more than 8 times will send "ATE1" with the UART set to 19200(!) baud on the Arduino side in 10s intervals, then switch the Arduino to 38400 baud, the communication is established and will last to the next power cycle.
I have no clue at all what might be causing this.
Anyone has got an idea?