* The reception is aborted if the stop bit does not arrive on schedule. * Waiting one bit time, then sampling the stop bit. * Waiting one bit time, then sampling bit 7. * Waiting one bit time, then sampling bit 6. * Waiting one bit time, then sampling bit 5. * Waiting one bit time, then sampling bit 4. * Waiting one bit time, then sampling bit 3. * Waiting one bit time, then sampling bit 2. * Waiting one bit time, then sampling bit 1. Received all the data, go wait for the STOP bit. * When it's time, shift in the data to the RX buffer. * Waiting one bit time, then sampling the LSb (bit 0). * Reject if the start bit does not last long enough */ * provides time offset for sampling future bits in the middle of the bit time. * Sampling the start bit a few more times to make sure it's solid. * Sampling continuously, waiting for the start bit. * true if a character is ready in soft_uart_rx_buf The caller need only invoke the function using the pointer. * This is implemented as a pointer to a function to handle the current * timebase at a fixed multiple of the bit rate. Static bool st_abort_wait_for_idle (bool) If the interrupt rate isĪ bit high relative to the baud rate, we want to sample late to This defines the phase shift of subsequent samples. ** The number of times to sample the start bit. * UART receiver is supported in a given project. * to be accessed directly by the calling code. * For speed, the receive buffer is implemented as a global variable that is * -# We repeat until we have sampled all data (payload) bits. * -# We sample and save the data bit, then wait (frequency multiplier - 1) * This puts us in the middle of the first data bit. * -# We delay (frequency multiplier) cycles, ignoring the state of the line. * -# We continue to sample the start bit until we have reached the center of * or fourth, depending on the setting) time with the expectation that the * -# Just to make sure it wasn't noise, we sample the line a second (or third * -# We sample the line continuously until the START (logic zero) bit is seen. * Here is an explanation of how a character is received: * | | Start bit | Data bit 0 | | Data bit N | Stop bit | * The sample timing error at the stop bit is (4% X 9) = 36% too early. * slower, owing to the fact that the system interrupy is not an exact multiple * The diagram below shows the resultant timing. * to sample slightly later in the bit time if possible.
* sample earlier and earlier on each successive bit. * Since the baud rate is high in this example, We will have a tendency to
UART EMBEDDED C PROGRAM SERIAL
* sample rate is four times the serial data bit rate: * Any frequency multiple of at least 3 is suitable. However, this receiver is designed to be configurable so * The baud rate of the transmitter constrains the ossortment of possible * been received and places the received character in a fixed buffer. The function returns a flag to indicate that a character has * on a stable timebase at a frequency at least three times * of the I/O pin is passed as an argument to the state machine animation * The receiver is implemented as a polled finite state machine. * communications using polling ("bit banging"). * This module implements the receive engine for asynchronous serial Any time the function returns true, the latest character is immediately available in soft_uart_rx_buf. For a 1200 baud data rate, an interrupt of approximately 200 microseconds is suitable, as shown in this example.Īt each state, the function returns true if a character has been received, and false otherwise. a function pointer points to a decision function for the current state and is invoked directly from the system's periodic interrupt.
UART EMBEDDED C PROGRAM CODE
The code is implemented as a direct-vectored state machine, i.e. This is useful when you have to receive data from a second serial source but the microcontroller has only one hardware serial port.
UART EMBEDDED C PROGRAM SOFTWARE
This module decodes asynchronous serial data in software out of a periodic interrupt.
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