# Hl7800 Maximum logic high voltage on UART pin

**URL:** <https://forum.sierrawireless.com/t/hl7800-maximum-logic-high-voltage-on-uart-pin/27383>\
**Category:** Uncategorized\
**Created:** [July 6, 2022, 12:54am UTC](https://forum.sierrawireless.com/t/hl7800-maximum-logic-high-voltage-on-uart-pin/27383 "2022-07-06T00:54:11Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![infoeugine](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@infoeugine](https://forum.sierrawireless.com/u/infoeugine)\
**Post date:** [July 6, 2022, 12:54am UTC](https://forum.sierrawireless.com/t/hl7800-maximum-logic-high-voltage-on-uart-pin/27383/1 "2022-07-06T00:54:11Z")

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I am looking for maximum allowed logic high voltage for HL7800 on UART pins, I am trying to interface HL7800 to a controller which got logic high voltage level as 3.3v, need to know the maximum allowed voltage on RX,TX,CTS and RTS pins only.

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**Author:** ![jerdung](https://avatars.discourse-cdn.com/v4/letter/j/82dd89/32.png) [@jerdung](https://forum.sierrawireless.com/u/jerdung)\
**Post date:** [July 7, 2022, 9:42am UTC](https://forum.sierrawireless.com/t/hl7800-maximum-logic-high-voltage-on-uart-pin/27383/2 "2022-07-07T09:42:04Z")

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Hi @infoeugine,

According to the document, the maximum allowed voltage on the RX, TX, CTS and RTS pins is 1.8V (VGPIO).  
For more detail, you can refer to Table 3-3: Digital I/O Electrical Characteristics (1.80V) on page 27 and  
Table 4-7: UART1 Pin Description on page 46.

The attached document below:  
[Sierra Wireless™ HL78xx Product Technical Specification](https://source.sierrawireless.com/resources/airprime/hardware_specs_user_guides/sierra-wireless%e2%84%a2-hl78xx-product-technical-specification/#sthash.wzo9nOnR.dpbs)

Thanks,