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zacharytomlinson committed Nov 26, 2024
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Raspberry Limitation & How To Solve
===================================
The Raspberry present some challenges when comes to UART and Serial connections. In the specific:



The mini UART is a secondary low throughput UART intended to be used as a console. The mini Uart has the following features:

* 7 or 8 bit operation.
* 1 start and 1 stop bit.
* No parities.
* Break generation.
* 8 symbols deep FIFOs for receive and transmit.
* SW controlled RTS, SW readable CTS.
* Auto flow control with programmable FIFO level.
* 16550 like registers.
* Baudrate derived from system clock.


As per SAS documentation, for the connection, you need:

19.2 KBaud in a "wakeup" mode. The 11-bit data packet consists of one start bit, eight data bits, a
ninth ‘wakeup’ bit, and one stop bit.


As you can see, you will never be able to connect successfully to a machine using ONLY the Raspberry. Here how to solve this pickle.
Whether using your computer or a microcomputer, you will need a logic level shifter in order to communicate safely over
an RS-232 connection. There are two ways to go about setting up your system to reliably communicate with the SAS interface:

Solution 1
----------

Use an RS-232 to TTL logic level converter. We tested the `MAX3323 <https://www.mouser.com/ProductDetail/Analog-Devices-Maxim-Integrated/MAX3323EEPE%2b?qs=CDqwynd4ZNoRwc1iI5RFww%3D%3D>`_
Use an RS-232 to TTL logic level converter. We tested the
1) `MAX3323 <https://www.mouser.com/ProductDetail/Analog-Devices-Maxim-Integrated/MAX3323EEPE%2b?qs=CDqwynd4ZNoRwc1iI5RFww%3D%3D>`_
2) `TRS3237EIDBR <https://www.ti.com/product/TRS3237E/part-details/TRS3237EIDBR>`_
3) `TRS3232EIDR <https://www.ti.com/product/TRS3232E?keyMatch=TRS3232EIDR&tisearch=universal_search&usecase=OPN-ALT>`_

If you decide to create a custom circuit to work with a raspberry pi, remember to:

In case you decide to buy and use the MAX3323 remember to:
1) Update your machine:

.. code-block::
Expand Down Expand Up @@ -77,4 +59,4 @@ In case you decide to buy and use the MAX3323 remember to:
Solution 2
----------

Buy and use an USB to serial adapter, we tested this `one from Prolific <https://www.amazon.com/USB-Serial-Adapter-Prolific-PL-2303/dp/B00GRP8EZU/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.eT7IwLbFTyi5P6wiZqvnXrIsQpdtfPz_M46xtQa_S1I6h-lpFonAvq5YC5xJqm4vO8e3APmv6ZveRIHnEk3JvZ7RPORl8CFQWSUM226Dz0JssJAFQzWxU_Rk-YZaVXY5yPT9ZX-bqG0CDKUEzPruTJWEFg-ITUZtUOwr8KLTrvxvVg-ounmiZNAaizmQvxjrTdVozOF4iRbI5UF54oqfyn1obbD9whyaS_eGnl-TRcU.CRPZSqj6-D9E9pUJExtcBxGZd89oO6OAewGmvDxATTU&dib_tag=se&keywords=prolific%2Busb%2Bto%2Bserial&qid=1705598420&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1>`_ and works like a charm and nothing has to be done on raspberry.
Buy and use an USB to serial adapter, we tested this `one from Prolific <https://www.amazon.com/USB-Serial-Adapter-Prolific-PL-2303/dp/B00GRP8EZU/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.eT7IwLbFTyi5P6wiZqvnXrIsQpdtfPz_M46xtQa_S1I6h-lpFonAvq5YC5xJqm4vO8e3APmv6ZveRIHnEk3JvZ7RPORl8CFQWSUM226Dz0JssJAFQzWxU_Rk-YZaVXY5yPT9ZX-bqG0CDKUEzPruTJWEFg-ITUZtUOwr8KLTrvxvVg-ounmiZNAaizmQvxjrTdVozOF4iRbI5UF54oqfyn1obbD9whyaS_eGnl-TRcU.CRPZSqj6-D9E9pUJExtcBxGZd89oO6OAewGmvDxATTU&dib_tag=se&keywords=prolific%2Busb%2Bto%2Bserial&qid=1705598420&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1>`_ and works like a charm and no modifications required on RPi.

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