RS-485 Communication 구현

RS-485 Communication Line 구현

1. 현재는 UART로 통신하는 기계를 Noise Robustness와 N:N Communication을 위해서 hardware와 software를 구현하는 과정을 적는다.

2. 메인 통신 모듈은 Teensy 3.5 (pin 버젼)이며, RS-485 Transceiver는 SP3485의 Breakout 모듈을 사용한다.

3. Digikey Order 내역 (1~2주 정도 걸림)

- SP3485 Transceiver, RS-485 Interface Evaluation Board: 1568-1589-ND

Datasheet: https://www.sparkfun.com/datasheets/Components/General/sp3485CN-LTR.pdf
Schematics of the Module: https://cdn.sparkfun.com/datasheets/BreakoutBoards/RS485_Breakout_v10.pdf

RS-485 모듈

SP3485 Schematics

- Teensy 3.5: 1568-1464-ND

Datasheet1: Find MK64FX512VMD12 at NXP

Datasheet2: https://media.digikey.com/pdf/Data%20Sheets/Sparkfun%20PDFs/DEV-14056_Web.pdf

Tutorials:

https://www.pjrc.com/teensy/tutorial.html

https://www.pjrc.com/teensy/pins.html

https://www.pjrc.com/teensy/usb_debug_only.html

Teensy 3.5 with Hearders

Teensy 3.5 Pin Map (Frontside)

Teensy 3.5 Pin Map (Backside)

4. pySerial + Arduino

현재 회사에서 주로 사용하는 툴은 Arduino sketch이며, 본인이 사용하는 언어는 Python이라서 두 개를 동시에 개발해보자.

5. pySerial

class serial.Serial

__init__(port=None, baudrate=9600, bytesize=EIGHTBITS, parity=PARITY_NONE, stopbits=STOPBITS_ONE, timeout=None, xonxoff=False, rtscts=False, write_timeout=None, dsrdtr=False, inter_byte_timeout=None)¶

- Parameters:
port – Device name or None.
baudrate (int) – Baud rate such as 9600 or 115200 etc.
bytesize – Number of data bits. Possible values: FIVEBITS, SIXBITS, SEVENBITS, EIGHTBITS
parity – Enable parity checking. Possible values: PARITY_NONE, PARITY_EVEN, PARITY_ODD PARITY_MARK, PARITY_SPACE
stopbits – Number of stop bits. Possible values: STOPBITS_ONE, STOPBITS_ONE_POINT_FIVE, STOPBITS_TWO
timeout (float) – Set a read timeout value.
xonxoff (bool) – Enable software flow control.
rtscts (bool) – Enable hardware (RTS/CTS) flow control.
dsrdtr (bool) – Enable hardware (DSR/DTR) flow control.
write_timeout (float) – Set a write timeout value.
inter_byte_timeout (float) – Inter-character timeout, None to disable (default).
Raises:
ValueError – Will be raised when parameter are out of range, e.g. baud rate, data bits.
SerialException – In case the device can not be found or can not be configured.

open()
Open port.

close()
Close port immediately.

read(size=1)
Parameters: size – Number of bytes to read.
Returns: Bytes read from the port.
Return type: bytes

Read size bytes from the serial port.


write(data)
Parameters: data – Data to send.
Returns: Number of bytes written.
Return type: int
Raises SerialTimeoutException:
  In case a write timeout is configured for the port and the time is exceeded.


flush()

Flush of file like objects. In this case, wait until all data is written.

reset_input_buffer()
Flush input buffer, discarding all it’s contents.

Changed in version 3.0: renamed from flushInput()

reset_output_buffer()
Clear output buffer, aborting the current output and discarding all that is in the buffer.


Changed in version 3.0: renamed from flushOutput()

rts
Setter: Set the state of the RTS line
Getter: Return the state of the RTS line
Type: bool
Set RTS line to specified logic level. It is possible to assign this value before opening the serial port, then the value is applied uppon open().

dtr
Setter: Set the state of the DTR line
Getter: Return the state of the DTR line
Type: bool
Set DTR line to specified logic level. It is possible to assign this value before opening the serial port, then the value is applied uppon open().