Access Functions

The first byte of a ThingSet message is either a text-mode identifier (?, =, !, +, -, : and #), a binary request code or a binary status code. Received data with unknown first byte is ignored, so that other text output (e.g. debug print information) can be used in parallel to the ThingSet protocol on the same serial interface.


The protocol supports the typical CRUD operationsopen in new window. Request codes match with CoAP to allow transparent mapping between ThingSet and HTTP APIs or CoAP devices.

CodeText IDMethodDescription
0x01?GETRetrieve all data from a path
0x02+ or !POSTAppend data to an object or execute a function
0x04-DELETEDelete data from an object
0x05?FETCHRetrieve a subset of data from a path
0x07=iPATCHUpdate (overwrite) data of a path

The CoAP PUT and PATCH methods are not explicitly implemented. PUT is equivalent to an update of all sub-objects of a resource using a PATCH request. PATCH requests for ThingSet are always idempotent, so only the iPATCH request code is supported. The two different text IDs for POST requests are synonyms. It is decided based on the type of the data object if the request is understood as a function call or a request to create a resource.

Additional request codes may be introduced in the future. Codes 0x0A, 0x0D and 0x20-0x7F are reserved, as they represent the ASCII characters for readable text including LF and CR.


Response messages in binary format are identified by a first byte greater than or equal to 128 (0x80) containing a status code which shows if the request could be handled successfully. For status codes between 0x80 and 0x9F, the response was successful. If the status code is greater than or equal to 0xA0, an error occured.

The status codes are again aligned with CoAP response codes, but contain an offset so that there is no interference with ASCII characters (less than 0x80).

0x812.01201CreatedAnswer to POST requests appending data
0x822.02204DeletedAnswer to DELETE request
0x832.03200ValidAnswer to POST requests to exec objects
0x842.04204ChangedAnswer to PATCH requests
0x852.05200ContentAnswer to GET / FETCH requests
0xA04.00400Bad Request
0xA14.01401UnauthorizedAuthentication needed
0xA34.03403ForbiddenTrying to write read-only value
0xA44.04404Not Found
0xA54.05405Method Not AllowedIf e.g. DELETE is not allowed for that object
0xA84.08400Request Entity Incomplete
0xA94.09409ConflictConfiguration conflicts with other settings
0xAD4.13413Request Entity Too Large
0xAF4.15415Unsupported Content-FormatIf trying to assign a string to an int
0xC05.00500Internal Server Error
0xC15.01501Not Implemented

The text mode converts the the hexadecimal response code into a string without the 0x prefix. The binary mode uses the code directly as the first byte.


Statements are neither requests nor response messages, as they are sent without expecting a confirmation. Below table lists the message specifier in text and binary mode.

CodeText IDDescription
0x1F#Statement message

The internal path _pub is used to configure the device to publish certain data items on a regular basis through a defined communication channel (UART, CAN, LoRaWAN, etc.). If implemented in the firmware, the publication interval may be adjustable.

By convention, the object names below the _pub define which data object should be published. This can be an entire group like Bat or a subset data object that contains a list of references to other data items like eChange in the above example.

More details regarding the ThingSet protocol methods for data access will be explained in the next chapter.

Idea for evaluation

Publication of a statement can be manually triggered by sending the statement with empty payload to that device.