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I have an ADH8066 GSM module that I'm trying to get up and running. I'm powering it with 4V (via a 2A adjustable regulator), and I'm using a Bus Pirate connected to its RX0 and TX0 lines. I'm not using RTS/DSR/CTS, because the datasheet says it doesn't do flow control by default. I do have a SIM card installed, but it's a non-activated one. I don't expect that to make a difference to whether or not the UART interface is available.

I'm pulling ONKEY low for about 2 seconds to turn it on. It's powering up, and I get the following output:

IIII
SystemInit
+ADSYS: BK=0x1,0x11, RV=0x1, Fail=0x0
+ADSYS: FLASH VERIFY OK

Ready

However, it doesn't seem to accept any input. I believe that remote echo is turned on by default, but I get nothing echoed back to me. AT does not result in OK, and no other informational command gives me any output. I've sent commands with explicit "AT+CGMM" 13 10 to ensure the line ending is correct.

During all this, GPIO10 (ready for AT command) remains low. The datasheet doesn't say which state is active, but I'm assuming active high based on some people's LED wiring.

Is there something else I'm not doing?

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The solution, it turns out, is to tie DSR0 to ground. The module then happily accepts commands. Thanks to the schematic of SparkFun's evaluation board for that one. It's a shame that the documentation on this module is so weak.

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There are a few suggestions I can think of, the first is to try sending a few CR/LF pairs at startup followed by the ATE1Q0 and see what that does. The power-up defaults don't seem to be explicitly stated in the datasheet but some GSM modules startup in quiet mode and won't respond to AT with an OK response.

The other time I've seen a GSM module go into that state is when there are power problems. The module starts up OK, tries to register on the network (even without a SIM card for emergency calls) and then the power dips. To maintain integrity on the the network they normally have a voltage monitor that will instantly shut down the module if that occurs even if for only a millisecond.

You're driving the module with a 4V 2A supply which sounds like a good choice but if you're using long wires to connect it place a reservoir cap near the module, maybe say 1000uF near the module to see if that makes a difference. That might be a good idea regardless, the datasheet only mentions typical current draws but often a GSM module will draw very short peak currents of around 2A.

You could also try powering it from a Li-Ion battery if you have one handy to take any problems with the power supply out of the equation. If you have a scope it would also be worth setting up a negative going trigger around 3.6V to see if you are getting any quick power dips.

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  • \$\begingroup\$ > try sending a few CR/LF pairs at startup followed by the ATE1Q0 and see what that does. Does nothing. The logic probe isn't even showing pulses on the TX0 line (which it does during the startup output), only the RX0 one. I realized I did have a 1.5A power supply attached, so I've replaced that with a 2.5A one, with no improvement. \$\endgroup\$ – Dan Ellis Jul 8 '13 at 21:28
  • \$\begingroup\$ @Derecho, do you have the bus pirate set for normal mode? If it's set for open collector you'd need a pull-up resistor. Ignore that I see you've sorted it out. \$\endgroup\$ – PeterJ Jul 9 '13 at 1:53

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