Arduino Software Serial Handshake
FISHINO: Arduino becomes wireless. Even if serial handshake lines are foreseen on ESP Software serial is simply too slow to overcome the limit of about 57.
A New Software Serial Library for Arduino
News: NewSoftSerial is in the core. Starting with Arduino 1.0 December, 2011, NewSoftSerial has replaced the old SoftwareSerial library as the officially supported software serial library. This means that if you have 1.0 or later, you should not download this library. To port your code to 1.0, simply change all NewSoftSerial references to SoftwareSerial.
NewSoftSerial is the latest of three Arduino libraries providing soft serial port support. It s the direct descendant of ladyada s AFSoftSerial, which introduced interrupt-driven receives – a dramatic improvement over the polling required by the native SoftwareSerial.
Without interrupts, your program s design is considerably restricted, as it must continually poll the serial port at very short, regular intervals. This makes it nearly impossible, for example, to use SoftwareSerial to receive GPS data and parse it into a usable form. Your program is too busy trying to keep up with NMEA characters as they arrive to actually spend time assembling them into something meaningful. This is where AFSoftSerial s and NewSoftSerial s interrupt architecture is a godsend. Using interrupt-driven RX, your program fills its buffer behind the scenes while processing previously received data.
NewSoftSerial offers a number of improvements over SoftwareSerial:
It inherits from built-in class Print, eliminating some 4-600 bytes of duplicate code
It implements circular buffering scheme to make RX processing more efficient
It extends support to all Arduino pins 0-19 0-21 on Arduino Mini, not just 0-13
It supports multiple simultaneous soft serial devices.
It supports a much wider range of baud rates.
It provides a boolean overflow method to detect buffer overflow.
Higher baud rates have been tuned for better accuracy.
It supports the ATMega328 and 168.
It uses direct port I/O for faster and more precise operation.
New with version 10. It supports software signal inversion.
New It supports 20MHz processors.
New It runs on the Teensy and Teensy.
New It supports an end method as a complement to begin.
But see below for an important caveat on multiple instances.
Be circumspect about using 300 and 1200 baud though. The interrupt handler at these rate becomes so lengthy that timer tick interrupts can be starved, causing millis to stop working during receives.
There has been considerable support for an library that would allow multiple soft serial devices. However, handling asynchronously received data from two, three, or four or more serial devices turns out to be an extremely difficult, if not intractable problem. Imagine four serial devices connected to an Arduino, each transmitting at 38,400 baud. As bits arrive, Arduino s poor little processor must sample and process each of 4 incoming bits within 26 microseconds or else lose them forever. Yikes.
It occurred to me, though, that multiple instances could still be possible if the library user were willing to make a small concession. NewSoftSerial is written on the principle that you can have as many devices connected as resource constraints allow, as long as you only use one of them at a time. If you can organize your program code around this constraint, then NewSoftSerial may work for you.
What does this mean, exactly. Well, you have to use your serial devices serially, like this:
// Here s a GPS device connect to pins 3 and 4
// A serial thermometer connected to 5 and 6
// An LCD connected to 7 and 8
NewSoftSerial LCD 8,7 ; // serial LCD
// collect data from the GPS unit for a few seconds
read_gps_data ; // use gps as active device
// collect temperature data from thermometer
read_thermometer_data ; // now use therm
// LCD becomes the active device here
In this example, we assume that read_gps_data uses the gps object and read_thermometer_data uses the therm object. Any time you call the listen method, it becomes the active object, and the previously active object is deactivated and its RX buffer discarded. An important point here is that object.available always returns 0 unless object is already active. This means that you can t write code like this:
This code will never do anything but activate one device after the other.
Normal TTL serial signaling defines a start bit as a transition from high to low logic. Logical 1 is high, 0 is low. But some serial devices turn this logic upside down, using what we call inverted signaling. As of version 10, NewSoftSerial supports these devices natively with a third parameter in the constructor.
NewSoftSerial myInvertedConn 7, 5, true ; // this device uses inverted signaling
NewSoftSerial myGPS 3, 2 ; // this one doesn t
You can retrieve the version of the NewSoftSerial library by calling the static member library_version.
int ver NewSoftSerial::library_version ;
Linking the NewSoftSerial library to your application adds approximately 2000 bytes to its size.
The latest version of NewSoftSerial is available here: NewSoftSerial12.zip. Note: don t download this if you have Arduino 1.0 or later. As of 1.0, NewSoftSerial is included in the Arduino core named SoftwareSerial.
ported to Arduino 0013, included example sketch in package
several important improvements: a support for 300, 1200, 14400, and 28800 baud see caveats, b added bool overflow method to test whether an RX buffer overflow has occurred, and c tuned RX and TX for greater accuracy at high baud rates 38.4K, 57.6K, and 115.2K.
minor bug fixes add. o file and objdump.txt to zip file for diagnostics.
etracer s inline assembler fix to OSX avr-gcc 4.3.0 interrupt handler bug added.
ladyada s new example sketch, fix to interrupt name, support for 328p.
etracer s workaround is now conditionally compiled only when avr-gcc s version is less than 4.3.2.
8 MHz support and flush and enable_timer0 methods added
digitalread/write scrapped in favor of direct port I/O. Revised routines now get perfect RX up to 57.6K on 16MHz processors and 31.25K on 8MHz processors.
inverted TTL signalling supported. 20MHz processors supported. Teensy and Teensy supported. New end method and destructor added to clean up.
added listen method to explicitly activate ports.
Many thanks to David Mellis, who wrote the original SoftwareSerial, and to the multi-talented ladyada, whose work with AFSoftSerial is seminal. Ladyada also provided the Goodnight, moon example sketch, fixed a problem with the interrupt naming see v6 and tested NSS with the 328p.
Thanks also to rogermm and several other forum users who have tested NewSoftSerial and given useful feedback.
The diligent analysis of forum user etracer yielded the root cause of a tricky problem with NSS on OSX. A bug in avr-gcc 4.3.0 causes the compiler to fail to generate the proper entry and exit sequences for certain interrupt handlers. etracer identified the problem and provided an inline workaround. etracer s fix is in NSS 5.
User jin contributed a large body of work based on NSS and identified a potential problem that could result in data loss fixed in NSS 5. jin also made a variant of NSS that supports 4-pin serial, with the additional pins providing a very nice RTS/CTS flow control. We may see this in NSS in the near future.
Thanks to Garret Mace, who contributed the delay tables for 20MHz processors and claims that he can send and receive at 115K baud. Cool.
Thanks to Paul Stoffregen, both for his fine work with Teensy and Teensy, and for contributing some useful suggestions that help NewSoftSerial run on them without modification.
I appreciate any and all input.
SoftwareSerial on Arduino Mega. up vote 4 down vote favorite. software serial. The SoftwareSerial library you refer to does not use the integrated UART hardware.
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