派︰《  》畫傳︰昔有『米勒』者繪作『拾穗』圖，──

拾穗一詞淵源於舊約聖經路得記-路得與波阿斯的記載，路得在波阿斯田裏撿麥穗，以供養她的婆婆拿俄米，指農民需讓貧苦人撿拾收割後遺留穗粒以求溫飽，而該畫除了描繪3名農婦在金黃色麥田撿拾麥穗情景外，其金黃陽光、彎腰等細節，另外呈現「英雄史詩般的崇高意境」。 畫面上三位年紀不同的女性，表現出勞動家庭的命運 ，且畫面遠處可看到農地監督者坐於馬背上觀看，反映出當時資本主義產生的貧富差距。 畫面因遠方地平線處的教堂而流露出一股近似宗教情操的崇高性。──

，觀之令人紅眼框。無巧不成書，無事難商量，想那《水滸傳》，真真是，官逼民反作強梁。

雖聞物已至，何故改課鋼，應應昨日事，補過先思量。一時講起了《通訊口》！殊不知早是議論紛紛！！

☿ 長︰同學們請安靜。據聞實習的材料已到，課表將略作調整 ，學長告知此事與駭黑之事無涉！請大家按新表操課。

 

☆ 編者言

當真應了 M♪o 的『巧』字，恰巧『樹莓派 SAKS 擴展板』上也有『序列埠』，更巧它還有『教程』，此時 M♪o 正巧寫及《通訊口》 ，果然巧遇巧成七巧的耶！！讀她那一句『學長告知……無涉』，真真是此地無銀三百兩，妙哉！妙哉！按新表操課！！

 

生︰《  》技引入門之徑︰

『樹莓派』也可以玩些不一樣的事情。由於我們將談談『序列埠』在『軟體學習』上的一些想法， 在此並不介紹基本的 Serial Port 之點點滴滴，特於此篇列出一些參考鏈結︰

‧ Raspberry Pi Serial Port

‧ RPi Serial Connection

‧ What is AMA in /dev/ttyAMA0

‧ Lesson 5. Using a Console Cable ── Adafruit’s Raspberry Pi

‧ How To: Use Minicom on Linux for Serial Port Comunication

希望讀者能夠自行閱讀。

 

☆ 編者言

由於《 Physical computing ︰《四》 Serial Port ︰ 1. 開宗明義》文中之

How To: Use Minicom on Linux for Serial Port Comunication 鏈結已僵，校而改之為

11.7 Using minicom and seyon

，故此記。

 

△ 《  》文講程式庫使用之法︰

pySerial

 

△  TTL serial 是什麼哩，還請參造︰

RS-232 vs. TTL Serial Communication

Skill Level: Beginner

by Jimb0 | November 23, 2010 | 7 comments

---

One of the tools we use most when debugging our projects is serial input/output. Serial is very easy to implement, and it allows you to send/receive any data you need from your microcontroller to a computer’s serial port so it can be viewed using a terminal emulator. These two devices are compatible from a software perspective, however you can’t just hook a microcontroller up to a computer because the hardware interfaces are not compatible.

Most microcontrollers these days have built in UARTs (universally asynchronous receiver/transmitter) that can be used to receive and transmit data serially. UARTs transmit one bit at a time at a specified data rate (i.e. 9600bps, 115200bps, etc.). This method of serial communication is sometimes referred to as TTL serial (transistor-transistor logic). Serial communication at a TTL level will always remain between the limits of 0V and Vcc, which is often 5V or 3.3V. A logic high (‘1’) is represented by Vcc, while a logic low (‘0’) is 0V.

The serial port on your computer (if it’s lucky enough to have one, they’re quickly becoming a relic) complies with the RS-232 (Recommended Standard 232) telecommunications standard. RS-232 signals are similar to your microcontroller’s serial signals in that they transmit one bit at a time, at a specific baud rate, with or without parity and/or stop bits. The two differ solely at a hardware level. By the RS-232 standard a logic high (‘1’) is represented by a negative voltage – anywhere from -3 to -25V – while a logic low (‘0’) transmits a positive voltage that can be anywhere from +3 to +25V. On most PCs these signals swing from -13 to +13V.

The more extreme voltages of an RS-232 signal help to make it less susceptible to noise, interference, and degradation. This means that an RS-232 signal can generally travel longer physical distances than their TTL counterparts, while still providing a reliable data transmission.

 

This timing diagram shows both a TTL (bottom) and RS-232 signal sending 0b01010101

 

碼︰讀 習。讀碼練習。

#!/usr/bin/env python

# Very simple serial terminal
# (C)2002-2004 Chris Liechti <cliecht@gmx.net>

# Input characters are sent directly (only LF -> CR/LF/CRLF translation is
# done), received characters are displayed as is (or as trough pythons
# repr, useful for debug purposes)
# Baudrate and echo configuartion is done through globals


import sys, os, serial, threading, getopt

EXITCHARCTER = '\x04'   #ctrl+D

#first choose a platform dependant way to read single characters from the console
if os.name == 'nt':
    import msvcrt
    def getkey():
        while 1:
            if echo:
                z = msvcrt.getche()
            else:
                z = msvcrt.getch()
            if z == '\0' or z == '\xe0':    #functions keys
                msvcrt.getch()
            else:
                if z == '\r':
                    return '\n'
                return z

elif os.name == 'posix':
    import termios, sys, os
    fd = sys.stdin.fileno()
    old = termios.tcgetattr(fd)
    new = termios.tcgetattr(fd)
    new[3] = new[3] & ~termios.ICANON & ~termios.ECHO
    new[6][termios.VMIN] = 1
    new[6][termios.VTIME] = 0
    termios.tcsetattr(fd, termios.TCSANOW, new)
    s = ''    # We'll save the characters typed and add them to the pool.
    def getkey():
        c = os.read(fd, 1)
        #~ c = sys.stdin.read(1)
        if echo: sys.stdout.write(c); sys.stdout.flush()
        return c
    def clenaup_console():
        termios.tcsetattr(fd, termios.TCSAFLUSH, old)
    sys.exitfunc = clenaup_console      #terminal modes have to be restored on exit...

else:
    raise "Sorry no implementation for your platform (%s) available." % sys.platform

CONVERT_CRLF = 2
CONVERT_CR   = 1
CONVERT_LF   = 0

def reader():
    """loop forever and copy serial->console"""
    while 1:
        data = s.read()
        if repr_mode:
            sys.stdout.write(repr(data)[1:-1])
        else:
            sys.stdout.write(data)
        sys.stdout.flush()

def writer():
    """loop and copy console->serial until EOF character is found"""
    while 1:
        c = getkey()
        if c == EXITCHARCTER: 
            break                       #exit app
        elif c == '\n':
            if convert_outgoing == CONVERT_CRLF:
                s.write('\r\n')         #make it a CR+LF
            elif convert_outgoing == CONVERT_CR:
                s.write('\r')           #make it a CR
            elif convert_outgoing == CONVERT_LF:
                s.write('\n')           #make it a LF
        else:
            s.write(c)                  #send character


#print a short help message
def usage():
    sys.stderr.write("""USAGE: %s [options]
    Miniterm - A simple terminal program for the serial port.

    options:
    -p, --port=PORT: port, a number, default = 0 or a device name
    -b, --baud=BAUD: baudrate, default 9600
    -r, --rtscts:    enable RTS/CTS flow control (default off)
    -x, --xonxoff:   enable software flow control (default off)
    -e, --echo:      enable local echo (default off)
    -c, --cr:        do not send CR+LF, send CR only
    -n, --newline:   do not send CR+LF, send LF only
    -D, --debug:     debug received data (escape nonprintable chars)

""" % (sys.argv[0], ))

if __name__ == '__main__':
    #initialize with defaults
    port  = 0
    baudrate = 9600
    echo = 0
    convert_outgoing = CONVERT_CRLF
    rtscts = 0
    xonxoff = 0
    repr_mode = 0
    
    #parse command line options
    try:
        opts, args = getopt.getopt(sys.argv[1:],
            "hp:b:rxecnD",
            ["help", "port=", "baud=", "rtscts", "xonxoff", "echo",
            "cr", "newline", "debug"]
        )
    except getopt.GetoptError:
        # print help information and exit:
        usage()
        sys.exit(2)
    
    for o, a in opts:
        if o in ("-h", "--help"):       #help text
            usage()
            sys.exit()
        elif o in ("-p", "--port"):     #specified port
            try:
                port = int(a)
            except ValueError:
                port = a
        elif o in ("-b", "--baud"):     #specified baudrate
            try:
                baudrate = int(a)
            except ValueError:
                raise ValueError, "Baudrate must be a integer number, not %r" % a
        elif o in ("-r", "--rtscts"):
            rtscts = 1
        elif o in ("-x", "--xonxoff"):
            xonxoff = 1
        elif o in ("-e", "--echo"):
            echo = 1
        elif o in ("-c", "--cr"):
            convert_outgoing = CONVERT_CR
        elif o in ("-n", "--newline"):
            convert_outgoing = CONVERT_LF
        elif o in ("-D", "--debug"):
            repr_mode = 1

    #open the port
    try:
        s = serial.Serial(port, baudrate, rtscts=rtscts, xonxoff=xonxoff)
    except:
        sys.stderr.write("Could not open port\n")
        sys.exit(1)
    sys.stderr.write("--- Miniterm --- type Ctrl-D to quit\n")
    #start serial->console thread
    r = threading.Thread(target=reader)
    r.setDaemon(1)
    r.start()
    #and enter console->serial loop
    writer()

    sys.stderr.write("\n--- exit ---\n")

 

☿ 行︰就這樣一股腦兒的胡倒，不知是教學，還是學教。☿☹只聽過背書，難不成背碼的耶！☿☹☹ 又沒給安裝之法，不知是要怎麼練哪樣習？咦！東西還沒見到，該裝…… ☿☺☿

 

訊︰ ☿ 子曰：『學而不思則罔，. 思而不學則殆』