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73 lines
2.4 KiB
ReStructuredText
73 lines
2.4 KiB
ReStructuredText
The USART Asynchronous Driver
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=============================
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The universal synchronous and asynchronous receiver and transmitter
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(USART) is usually used to transfer data from one device to the other.
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The USART driver use a ring buffer to store received data. When the USART
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raise the data received interrupt, this data will be stored in the ring buffer
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at the next free location. When the ring buffer is full, the next reception
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will overwrite the oldest data stored in the ring buffer. There is one
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USART_BUFFER_SIZE macro per used hardware instance, e.g. for SERCOM0 the macro
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is called SERCOM0_USART_BUFFER_SIZE.
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On the other hand, when sending data over USART, the data is not copied to an
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internal buffer, but the data buffer supplied by the user is used. The callback
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will only be generated at the end of the buffer and not for each byte.
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User can set action for flow control pins by function usart_set_flow_control,
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if the flow control is enabled. All the available states are defined in union
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usart_flow_control_state.
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Note that user can set state of flow control pins only if automatic support of
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the flow control is not supported by the hardware.
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Features
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--------
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* Initialization/de-initialization
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* Enabling/disabling
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* Control of the following settings:
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* Baudrate
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* UART or USRT communication mode
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* Character size
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* Data order
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* Flow control
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* Data transfer: transmission, reception
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* Notifications about transfer done or error case via callbacks
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* Status information with busy state and transfer count
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Applications
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------------
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They are commonly used in a terminal application or low-speed communication
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between devices.
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Dependencies
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------------
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USART capable hardware, with interrupt on each character is sent or
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received.
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Concurrency
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-----------
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Write buffer should not be changed while data is being sent.
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Limitations
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-----------
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* The driver does not support 9-bit character size.
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* The "USART with ISO7816" mode can be only used in ISO7816 capable devices.
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And the SCK pin can't be set directly. Application can use a GCLK output PIN
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to generate SCK. For example to communicate with a SMARTCARD with ISO7816
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(F = 372 ; D = 1), and baudrate=9600, the SCK pin output frequency should be
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config as 372*9600=3571200Hz. More information can be refer to ISO7816 Specification.
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Known issues and workarounds
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----------------------------
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N/A
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