Dummy byte is received when wakeup source is not UART

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ruha_3574251
Level 1
Level 1

Hello, I am struggling on the PSOC4 deepsleep. 0xFF is received when wakeup source is not UART. I find the UART low power note in the UART component datasheet.

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0xFF is gone after applying this workaround. But I have to add more preamble bytes before the real data. It is very inconvenient.

Is there a solution or workaround to  resolve this issue better?

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1 Solution

Hi ruilinhao_3574251​,

Thanks for the update. It is recommended to use 0x00 as the preamble byte for your application.

So when the device wakes up due to timer, PSoC will read even the preamble data. In such cases, you need to discard the packet when the data is 0x00. Do you face any difficulties in this? Please let us know.

Regards,

Bragadeesh

Regards,
Bragadeesh

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BragadeeshV
Moderator
Moderator
Moderator
First question asked 1000 replies posted 750 replies posted

Hi,

Both of these methods "Skip start bit" and "disable skip start bit" are suggested only when the UART is used as a wake up source. Not otherwise.

So there are two things you can do here:

1. Use UART as a wake up source. Depending on your data rate, you can choose between the two methods suggested in the datasheet

2. If you are not using UART as wake up source, you shouldn't send data to the UART RX unless the device has woken up. For which you can signal the other device that the device has woken up using the Tx pin and then receive the data.

Hope this helps!

Regards,

Bragadeesh

Regards,
Bragadeesh
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Hi Bragadeesh,

Thanks for you reply.

I am using both UART and Timer as my wake up source. If I choose "skip start", dummy data is received when timer wake up the deepsleep. And I will need to add preamble data if I disable the "skip start" feature. This is my question.

Regards,

Ruilin

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Hi ruilinhao_3574251​,

Thanks for the update. It is recommended to use 0x00 as the preamble byte for your application.

So when the device wakes up due to timer, PSoC will read even the preamble data. In such cases, you need to discard the packet when the data is 0x00. Do you face any difficulties in this? Please let us know.

Regards,

Bragadeesh

Regards,
Bragadeesh
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