RN4678 Does Not Enter Command Mode

Question

I've been trying to get the Microchip RN4678 bluetooth module working so I can start having fun with it, but I'm having very very limited success. The problem is the fact that the datasheet states:

To enter Command mode, type $$$ into the terminal emulator. Once RN4678 enters Command mode, it sends the string CMD via the UART to indicate the start of Command mode session.

I'm doing exactly that, along with every variation and am getting no response. Here's my setup. First things first I've got it plugged into a breadboard like this:

I'm using a stock TTL programmer based around the FTDI232R, and it's all being controlled and monitored from the OSX program Serial. Here's the settings I'm using in serial.

Observations from my troubleshooting so far:

1. The chip itself is working fine. I can connect to it through the mBIoT utility iPhone app, and it sends and transmits data from phone to computer and vice versa fine, so I know the module isn't dead.
2. The modules CTS pin doesn't get pulled low unless there is a paired connection. When my phone is connected I can pipe data through the RN4678 from computer to phone with hardware flow enabled just fine, but as soon as I disconnect my phone, I cannot talk to the module at all.
3. I've looked into the option of the modules "fast-mode" being activated by default, where the original "$$$" command doesn't work, and instead you have to pull a specific pin low. So I went around, and pulled each pin low individually and had no success.

Right now it just feels like theres a hidden pin in there that needs to be pulled in some sort of direction. I've had a good look at the Pictail Reference design for this module and I'm faily sure I haven't missed any pins.

If this is ringing any bells for anyone, or if you have any ideas I should try I'd really love your help. Here's the corresponding Datasheet and User Guide for this module.

Answer 1

I worked with RN4870 and it worked just fine for me after 2 months of debugging. It just takes time. When I did it, I didn't connect CTS or any other pin. I just had Vbat to 3.3V, Gnd, tx and rx. Rst is internally pulled high. Don't mess with it.

I see that you are sending 'LF' after your command. When sending that command you should not send LF or CR. The chip doesn't interpret it as a command for data mode. Deselect LF and try sending $$$. I had this problem when I was working on this. Let me know if this works.

Answer 2

P2_0 and P2_4 should be pulled high as you have in your schematic (but not necessary as the datasheet claims there are internal pull-ups), but the EAN pin (#20) needs to be pulled to GND for "Normal Operation / Application Mode". Refer to Table 2-1 in the datasheet. Your configuration where all lines are pulled high is undefined.

Answer 3

In the manual the pin "SW_BTN" doesn't has to be connected and is stated "default: disabled". But in reality this input has to be set to BAT_IN (3,3V) permanentely if the module should work!!

As stated above the EAN Pin has to be pulled to GND to enable "normal operating mode / command mode". The configuration in the following modified drawing is working fine (without the option to flash new firmware - in this case the signals P2_0, P2_4 & EAN need another signal configuration). Afterwards the module (RN4678) is running in "normal communication mode" but can be switched to command mode by sending "§§§CR" (CR = one sign) answered by "CMD> CRLF" (CRLF = two signs) and so on ...