ARM Technical Support Knowledge Articles

What is the purpose of the Stick Parity Select (SPS) bit in the UART's LCR_H register?

Applies to: PL011 UART

Answer

The Stick Parity Select (SPS) bit is used to set either a permanent '1' or a permanent '0' as parity when transmitting or receiving data, depending on the state of the Parity Enable (PEN, bit[1]) and Even Parity Select (EPS, bit[2]) bits in the same register. Its purpose is to typically indicate the first byte of a package. In some situations, this could be an address byte, for example when broadcasting data in a multi-drop RS-485 network. In such a network, only the addressed UART would respond to the data, the others would ignore the broadcast.

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