class UART -- 双工串行通信总线¶
UART实现标准UART / USART双工串行通信协议。在物理层，它包括2条线：RX和TX通信单元是一个字符（不与一个字符串混淆），可以是8或9位。
from pyb import UART uart = UART(1, 9600) # init with given baudrate uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
uart.read(10) # read 10 characters, returns a bytes object uart.read() # read all available characters uart.readline() # read a line uart.readinto(buf) # read and store into the given buffer uart.write('abc') # write the 3 characters
Construct a UART object on the given bus.
buscan be 1-6, or 'XA', 'XB', 'YA', or 'YB'. With no additional parameters, the UART object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See
initfor parameters of initialisation.
The physical pins of the UART busses are:
(TX, RX) = (X1, X2) = (PA0, PA1)
(TX, RX) = (X9, X10) = (PB6, PB7)
(TX, RX) = (Y1, Y2) = (PC6, PC7)
(TX, RX) = (Y9, Y10) = (PB10, PB11)
(TX, RX) = (X3, X4) = (PA2, PA3)
The Pyboard Lite supports UART(1), UART(2) and UART(6) only. Pins are as above except:
(TX, RX) = (X1, X2) = (PA2, PA3)
init(baudrate, bits=8, parity=None, stop=1, *, timeout=1000, flow=0, timeout_char=0, read_buf_len=64)¶
Initialise the UART bus with the given parameters:
baudrateis the clock rate.
bitsis the number of bits per character, 7, 8 or 9.
parityis the parity,
None, 0 (even) or 1 (odd).
stopis the number of stop bits, 1 or 2.
flowsets the flow control type. Can be 0,
UART.RTS | UART.CTS.
timeoutis the timeout in milliseconds to wait for writing/reading the first character.
timeout_charis the timeout in milliseconds to wait between characters while writing or reading.
read_buf_lenis the character length of the read buffer (0 to disable).
This method will raise an exception if the baudrate could not be set within 5% of the desired value. The minimum baudrate is dictated by the frequency of the bus that the UART is on; UART(1) and UART(6) are APB2, the rest are on APB1. The default bus frequencies give a minimum baudrate of 1300 for UART(1) and UART(6) and 650 for the others. Use
pyb.freqto reduce the bus frequencies to get lower baudrates.
Note: with parity=None, only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits are supported.
Read characters. If
nbytesis specified then read at most that many bytes. If
nbytesare available in the buffer, returns immediately, otherwise returns when sufficient characters arrive or the timeout elapses.
nbytesis not given then the method reads as much data as possible. It returns after the timeout has elapsed.
Note: for 9 bit characters each character takes two bytes,
nbytesmust be even, and the number of characters is
Return value: a bytes object containing the bytes read in. Returns
Read bytes into the
nbytesis specified then read at most that many bytes. Otherwise, read at most
Return value: number of bytes read and stored into
Read a line, ending in a newline character. If such a line exists, return is immediate. If the timeout elapses, all available data is returned regardless of whether a newline exists.
Return value: the line read or
Noneon timeout if no data is available.
Write the buffer of bytes to the bus. If characters are 7 or 8 bits wide then each byte is one character. If characters are 9 bits wide then two bytes are used for each character (little endian), and
bufmust contain an even number of bytes.
Return value: number of bytes written. If a timeout occurs and no bytes were written returns
Write a single character on the bus.
charis an integer to write. Return value:
None. See note below if CTS flow control is used.
Send a break condition on the bus. This drives the bus low for a duration of 13 bits. Return value:
On Pyboards V1 and V1.1
UART(3) support RTS/CTS hardware flow control
using the following pins:
(TX, RX, nRTS, nCTS) = (X3, X4, X2, X1) = (PA2, PA3, PA1, PA0)
UART(3)is on :
(TX, RX, nRTS, nCTS) = (Y9, Y10, Y7, Y6) = (PB10, PB11, PB14, PB13)
On the Pyboard Lite only
UART(2) supports flow control on these pins:
(TX, RX, nRTS, nCTS) = (X1, X2, X4, X3) = (PA2, PA3, PA1, PA0)
In the following paragraphs the term "target" refers to the device connected to the UART.
When the UART's
init() method is called with
flow set to one or both of
UART.CTS the relevant flow control pins are configured.
nRTS is an active low output,
nCTS is an active low input with pullup
enabled. To achieve flow control the Pyboard's
nCTS signal should be connected
to the target's
nRTS and the Pyboard's
nRTS to the target's
CTS: target controls Pyboard transmitter¶
If CTS flow control is enabled the write behaviour is as follows:
If the Pyboard's
UART.write(buf) method is called, transmission will stall for
any periods when
False. This will result in a timeout if the entire
buffer was not transmitted in the timeout period. The method returns the number of
bytes written, enabling the user to write the remainder of the data if required. In
the event of a timeout, a character will remain in the UART pending
number of bytes composing this character will be included in the return value.
UART.writechar() is called when
False the method will time
out unless the target asserts
nCTS in time. If it times out
will be raised. The character will be transmitted as soon as the target asserts
RTS: Pyboard controls target's transmitter¶
If RTS flow control is enabled, behaviour is as follows:
If buffered input is used (
read_buf_len > 0), incoming characters are buffered.
If the buffer becomes full, the next character to arrive will cause
nRTS to go
False: the target should cease transmission.
nRTS will go
characters are read from the buffer.
Note that the
any() method returns the number of bytes in the buffer. Assume a
buffer length of
N bytes. If the buffer becomes full, and another character arrives,
nRTS will be set False, and
any() will return the count
characters are read the additional character will be placed in the buffer and will
be included in the result of a subsequent
If buffered input is not used (
read_buf_len == 0) the arrival of a character will
nRTS to go
False until the character is read.