# Hl78 no at response to mcu through uart 1

**URL:** <https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174>\
**Category:** HL78\
**Created:** [April 25, 2024, 9:14pm UTC](https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174 "2024-04-25T21:14:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![lsmtech](https://avatars.discourse-cdn.com/v4/letter/l/ac91a4/32.png) [@lsmtech](https://forum.sierrawireless.com/u/lsmtech)\
**Post date:** [April 25, 2024, 9:14pm UTC](https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174/1 "2024-04-25T21:14:05Z")

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I currently have my stm host device connected with the hl78 through uart1. I have tx,rx, rts, and cts. However I do not get any response back.  
When I use the terminal on my computer and connect the usb to the uart1 of the hl78, it works perfectly. Are there any additional set up that I need for an stm host device to work? Any switches or jumpers I need to set the hl78?

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**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:** [April 26, 2024, 2:55am UTC](https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174/2 "2024-04-26T02:55:37Z")

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if it works with PC UART, probably there is no problem with the module, then you need compare the voltage of those 4 lines

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**Author:** ![lsmtech](https://avatars.discourse-cdn.com/v4/letter/l/ac91a4/32.png) [@lsmtech](https://forum.sierrawireless.com/u/lsmtech)\
**Post date:** [April 29, 2024, 4:15pm UTC](https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174/3 "2024-04-29T16:15:56Z")

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I have yet to check the voltages, but I was wondering if there was a specific character that I needed to end the string when sending an at command over uart? Like do I end the string with a “\r\n” to indicate a return or do I need a “\0”? I have tried all of those combinations at the end of the string but is there something I am missing?

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**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:** [April 29, 2024, 4:29pm UTC](https://forum.sierrawireless.com/t/hl78-no-at-response-to-mcu-through-uart-1/32174/4 "2024-04-29T16:29:32Z")

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you should be able to find the answer in the case in your PC, right?