Download Komik Crayon Shinchan3/23/2021
Packet Structure Field Length SOH (Start Of Header) 5 Destination Address 1 Sender Address 1 Command 1 Data Length in Bytes 1 Packet Type 1 STX (Start Text) 1 Data X ETX (End Text) 1 Checksum 1 EOT (End Of Transmission) 1 The table above shows the basic structure of packets.JSON seems overkill, and a lot of work for the arduino to do.
Komik Crayon Shinchan Serial Port LookingI had the arduino to listen for a 2 character ascii command followed by a line feed (or was it carriage return) (GU n for Get Update), then the arduino would send: 0x02 n (ascii STX, start of transmission) IT t73.8 n IH t54.3 n 0x03 n (ascii ETX, end of transmission) I wrote a python function that sat and read the serial port looking for STX, then decoding each line until it got the ETX, at which point it would return (and then it would do whatever with the data).Anything that was not STX or ETX was considered data, with the first part identifying the data (IT for inside temperature), followed by a tab, then the value of the data.
In the elder days before the web, back even to the days when dinosaur mainframes ruled the earth in the late 60s (fifty years ago), the ASCII standard was developed to facilitate a standard of communication between machines, itself based upon the even more ancient and eldrich teletype codes. The first 32 characters of ASCII were non-printable control characters, use to communicate meta-information related to the messages being passed back and forth. The wheels of time turned, and the uses for many of these control characters became unfashionable and obsolete, but some live on in protocols in use even today (SYN ACK NAK in TCPIP), a sort of relic in the DNA of the modern descendants of those ancient Honeywell and Sperry Univac and Control Data machines. STX (start of text) and ETX (end of text) were standard ways to mark the begin and end of a messages content, often used in serial protocols. I dont know if anyone in the arduino community uses the old serial control characters, but they work perfectly for this use. Recently, weve been working on a large internet connected machine. This involves quite a large amount of electronics to drive all its motors, actuators and sensors. Komik Crayon Shinchan Upgrade We RedesignedIn a recent upgrade we redesigned the electronics and ended up using a system distributed across multiple arduinos, necessitating a communication protocol which could be used on an RS-485 topology. Availbale Arduino Libraries So whats the best serial communication library available on the arduino To start with, there are already some libraries in existence, most notably modbus. Komik Crayon Shinchan How To Use ItUnfortunately, the on arduino is fairly complex and its not immediately obvious how to use it best (edit: the library has actually been refactored and now looks much cleaner). Its very much written to interface with existing modbus equipment and not to build new devices.Obviously that would be the library of choice if we needed Modbus compatibility but given the freedom we had, there had to be a more modern, simpler option. Perusing github shows relatively little in the way of arduino - arduino communcation libraries, especially libraries tailored for RS-485 and hardened for reliability. Is one option and the packet format was the inspiration for our library, but it wasnt quite what we wanted. So we decided to pull the best parts of a few libraries together and roll them into something slightly more user friendly and modern. The SuperSerial Library So, what kind of topology should be used. In our case, we had a very obvious master slave layout: one arduino was connected to our server and would receive commands via the internet, all the other arduinos would be controlling some sensors and actuators and would need to run commands in parallel, responding to the master device when necessary. Now, the RS-485 chips we are using operate with a RX TX enable. The limitation is that two slaves cannot send data at exactly the same time, so a host or master based architecture is the most obvious mode of operation. The master polls each slave and wont send another poll out until it receives a response or times out. For lengthy operations, this can happen repeatedly until the slave finishes the operation, and multiple slaves can be polled in quick succession to give the illusion of parallelism.
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