Sales through fiscal devices cannot be equated to a simple printing process in a regular ESC/POS printer. The calculations are delegated to fiscal devices which are inspected and certified before being released onto the market. 

For the sake of avoiding a troubles, several algorithms are presented in this article. They are used by the most widely-employed fiscal devices in Bulgaria - made by Datecs Ltd.

The article describes a fiscal device communication protocol. It concerns two modifications to this protocol, which are characteristic of some of the most-widely used on the market models of fiscal devices manufactured by Datecs Ltd. You can find links to other articles describing the technologies and terms used in this article. Clarifications on the types of synchronisation, the format of packaged messages and the differences between the two modifications are provided.

If you are still interested, you can find the article here.

An article with a brief introduction on the topic. Definitions, advantages and disadvantages, approaches to developing device-dependent and device-independent software and my personal preferences.