S19 file contains low-level machine code in text format. S19 files are used for passing instructions to some types of Freescale microcontrollers. Freescale chips are commonly used by both professional manufacturers and amateurs.

S19 files store data in as records placed lin by line. Each line (except the last) starts with ‘S1’ expression/declaration. Data in S19 file is stored as hexidecimal binary data.