# UART AT Command hang when make a phone call **URL:** \ **Category:** RC76\ **Created:** [July 23, 2021, 1:11pm UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353 "2021-07-23T13:11:42Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![nguyenducminh](https://avatars.discourse-cdn.com/v4/letter/n/a6a055/32.png) [@nguyenducminh](https://forum.sierrawireless.com/u/nguyenducminh)\ **Post date:** [July 23, 2021, 1:11pm UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/1 "2021-07-23T13:11:43Z")
We are using RC7620 to make a phone call using ATD… When the callee answers the RC7620 does not return the CONNECT response via UART interface. We need to send another command AT to the module to get back the CONNECT response. However, when we disable the CMUX mode using the command AT!MUXMODE=0, the module responses intermediately. But disable the CMUX mode makes the module can not response to any all protocol commands at all. In our hardware design we leave the USB\_D+/- open. If we connect the module with USB so that the USB\_D+/- is connected, then the module responses. So we do NOT understand what happened to the UART protocol interface. Any advise is very appreciated. ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 24, 2021, 11:37am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/2 "2021-07-24T11:37:14Z")
I don’t see problem in UART port: ```auto ati3 Manufacturer: Sierra Wireless, Incorporated Model: RC7620 Revision: SWI9X07H_00.08.07.00 0ce4c1 jenkins 2021/03/17 02:18:20 IMEI: 353634110000980 IMEI SV: 17 FSN: 7Q9472000710AA +GCAP: +CGSM OK at+creG? +CREG: 0,1 OK atd93122509; OK CONNECT ath OK at!muxmode? !MUXMODE: 1 OK ``` ---
**Author:** ![nguyenducminh](https://avatars.discourse-cdn.com/v4/letter/n/a6a055/32.png) [@nguyenducminh](https://forum.sierrawireless.com/u/nguyenducminh)\ **Post date:** [July 25, 2021, 5:26am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/3 "2021-07-25T05:26:55Z")
Hi Jyijyi, Thank you for your response. Could you share me the hardware that you used? In my case, I use the development kit. The problem occurred only when the kit is powered by battery. If the kit is connected with a PC, the problem did not occur. I guested that when USB\_D+,D- are connected, there is no issue. With best regards, M. ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 5:42am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/4 "2021-07-25T05:42:18Z")
I used HL dev kit … ---
**Author:** ![nguyenducminh](https://avatars.discourse-cdn.com/v4/letter/n/a6a055/32.png) [@nguyenducminh](https://forum.sierrawireless.com/u/nguyenducminh)\ **Post date:** [July 25, 2021, 6:21am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/5 "2021-07-25T06:21:43Z")
Do you connect the Kit with the PC via USB? We used Mango Yellow. ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 6:25am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/6 "2021-07-25T06:25:51Z")
No, i do not connect usb ---
**Author:** ![nguyenducminh](https://avatars.discourse-cdn.com/v4/letter/n/a6a055/32.png) [@nguyenducminh](https://forum.sierrawireless.com/u/nguyenducminh)\ **Post date:** [July 25, 2021, 6:33am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/7 "2021-07-25T06:33:33Z")
Can you provide me the model of your HL Dev kit? ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 6:56am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/8 "2021-07-25T06:56:32Z")
It looks like this board [https://www.digikey.hk/product-detail/en/sierra-wireless/HL-DEV-KIT-6000620/1645-1011-ND/5843808?cur=HKD&lang=en](https://www.digikey.hk/product-detail/en/sierra-wireless/HL-DEV-KIT-6000620/1645-1011-ND/5843808?cur=HKD&lang=en) ---
**Author:** ![nguyenduchieu](https://avatars.discourse-cdn.com/v4/letter/n/43a26b/32.png) [@nguyenduchieu](https://forum.sierrawireless.com/u/nguyenduchieu)\ **Post date:** [July 25, 2021, 7:05am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/9 "2021-07-25T07:05:09Z")
Hi jyijyi I used kit Mangoh Yellow, powered by battery from CN1000 and not pluged USB, there was same problem. and when I pluged usb connector, problem was sloved. From Mangoh Yellow schematic, I see the only difference is that USB\_D+, USB\_D- are connected to the PC. Please help. Thanks ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 7:56am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/10 "2021-07-25T07:56:02Z")
Does the module go to sleep mode if no usb is connected? ---
**Author:** ![nguyenduchieu](https://avatars.discourse-cdn.com/v4/letter/n/43a26b/32.png) [@nguyenduchieu](https://forum.sierrawireless.com/u/nguyenduchieu)\ **Post date:** [July 25, 2021, 8:29am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/11 "2021-07-25T08:29:05Z")
yes. I used AT+KSLEEP=2 before ATD… ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 12:26pm UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/12 "2021-07-25T12:26:28Z")
does problem happen if setting AT+KSLEEP=1 ? ---
**Author:** ![toan\_tran123](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@toan\_tran123](https://forum.sierrawireless.com/u/toan_tran123)\ **Post date:** [July 25, 2021, 2:28pm UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/13 "2021-07-25T14:28:08Z")
Hi, The problem still happens with AT+KSLEEP=1, Thanks ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 25, 2021, 3:52pm UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/14 "2021-07-25T15:52:46Z")
for AT+KSLEEP=2 or AT+KSLEEP=1, you can workaround the issue by keep sending AT after “ATD1234567;” Is it correct? Another way you can try is to use AT+KSLEEP=0, after "ATD1234567; ", you can pull down the DTR and pull up the DTR again. ---
**Author:** ![nguyendinhlieu](https://avatars.discourse-cdn.com/v4/letter/n/bcef8e/32.png) [@nguyendinhlieu](https://forum.sierrawireless.com/u/nguyendinhlieu)\ **Post date:** [July 26, 2021, 2:02am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/15 "2021-07-26T02:02:14Z")
Hi, As i see, HL dev kit which you used just using for HL branch. Please check. ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 26, 2021, 2:04am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/16 "2021-07-26T02:04:19Z")
but I found that I can use it to communicate with RC module via USB and UART ---
**Author:** ![nguyenduchieu](https://avatars.discourse-cdn.com/v4/letter/n/43a26b/32.png) [@nguyenduchieu](https://forum.sierrawireless.com/u/nguyenduchieu)\ **Post date:** [July 26, 2021, 8:58am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/17 "2021-07-26T08:58:26Z")
Do you have schematic of your kit? I can’t find it, please share it with me ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 26, 2021, 9:01am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/18 "2021-07-26T09:01:52Z")
No, I don’t have, but I think I can see same issue. After I dial the call by ATD, if the receiver side does not answer too quickly, I can see same issue. that is why I suggest you to keep typing AT and see if you can still see this issue. ---
**Author:** ![nguyendinhlieu](https://avatars.discourse-cdn.com/v4/letter/n/bcef8e/32.png) [@nguyendinhlieu](https://forum.sierrawireless.com/u/nguyendinhlieu)\ **Post date:** [July 26, 2021, 9:32am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/19 "2021-07-26T09:32:11Z")
Yep, when it stuck, you can ping “AT” or any AT command to get respond from RC but We can not ping AT continuously, we don’t know when it has problem. And we find out that stuck can occur in many other case. So we need correct this problem from root cause. Thank you. ---
**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/jyijyi/32/4766_2.png) [@jyijyi](https://forum.sierrawireless.com/u/jyijyi)\ **Post date:** [July 26, 2021, 9:38am UTC](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353/20 "2021-07-26T09:38:01Z")
how about this one? you can try is to use AT+KSLEEP=0, after "ATD1234567; ", you can pull down the DTR and pull up the DTR again and see if the port is stuck. [Next page](https://forum.sierrawireless.com/t/uart-at-command-hang-when-make-a-phone-call/24353.md?page=2)