If the device is a CC3200, it is required to MUX the UART lines from the internal application processor ( Arm® Cortex®-M4) to the network processor.

The procedure for switching UART lines in CC3200 case follows:

1. The main processor sends the Switch UART to APPS MCU command. The user must provide the delay until the network processor is ready. One second is sufficient and should be used. During this time, the UART lines are switched, and the network processor is rebooted into bootloader mode. The reset is internal so the user does not need to externally apply it.
2. The CC3200 device responds with an Ack. This is the command response.
3. The main processor should send a break signal (sending continuous Spacing values [no Start or Stop bits]) on the CC3200 UART RX line. The network processor must sense this break signal during power up.
4. Because there are cases in which the break signal is missed or the Ack packet is being missed, TI recommends sending the break signal up to four times. Follow the following pseudocode for details.
5. The network processor responds with an Ack. This response is an indication that the network processor sensed the break signal and entered bootloader mode.
6. The main processor deasserts the break signal.

   For i=1..4
   set BREAK sleep 100mSec read ACK
   unset BREAK
   If successful break
   Else continue
   

Figure 5-4 shows the Switch UART to APPS MCU command and the Ack command response.

Figure 5-4 Switch UART Lines to APPS MCU Command

Figure 5-5 shows the BREAK assertion and deassertion followed by an Ack.

Figure 5-5 Switch UART to APPS MCU Procedure