What is the S19 file format?
.s19 files are text-based firmware encoding files using the Motorola S-record (SREC) format, created by Motorola in the 1970s for the 6800 microprocessor series. They encode binary firmware data as lines of ASCII hex records, making them human-readable, portable and editable in any text editor.
An .s19 file specifically uses 16-bit addressing (S1 data records and S9 end record), which limits the addressable range to 64 KB. For larger firmware images, the related formats .s28 (24-bit, S2/S8 records) and .s37 (32-bit, S3/S7 records) are used instead.
Each line follows a fixed structure: a record-type identifier (S0 for header, S1 for data, S9 for end-of-file), a byte count, a 2-byte address in ASCII hex, the data payload, and a 1-byte ones-complement checksum. This self-checking design lets flash programmers verify data integrity record by record before writing to device memory.
.s19 files are widely used in embedded systems development for programming microcontrollers in NXP (formerly Freescale/Motorola) families such as Kinetis, ColdFire, HCS08, HC11 and HC12. The srec_cat and srec_info utilities from the SRecord toolset are standard tools for converting, merging and validating SREC files. The Intel HEX format is the main alternative with comparable capabilities.
Security & safety
RISK: LOWS19 files are plain ASCII text; they cannot execute on a PC. Risk is contextual: flashing a wrong/corrupted S19 to a microcontroller can brick the device. Always verify checksum integrity and target compatibility before programming.
Format details
in a nutshellPrograms that open S19 files
Windows4 apps
Notepad
Open-source Open the file directly - displays human-readable ASCII hex records. Useful for inspection. 
SRecord (srec_cat / srec_info)
Open-source Command-line: srec_info firmware.s19 to inspect; srec_cat to convert/merge/split SREC files.
Keil MDK / uVision
Freemium Configure output to .s19 in project settings; use flash-download feature to program target. 
macOS1 app
SRecord (srec_cat)
Open-source Install via Homebrew (brew install srecord); srec_info file.s19 to inspect. 
Linux2 apps
SRecord (srec_cat)
Open-source apt install srecord; srec_info file.s19 to verify and inspect records.
GCC + objcopy
Open-source objcopy -O srec firmware.elf firmware.s19 (generate); objcopy -I srec -O binary to convert to binary. Technical details
deep spec| Encoding | ASCII text (7-bit), line-delimited records; editable in any text editor |
| Address width | 16-bit (S1/S9 records); maximum 64 KB addressable per file |
| Record types | S0 (header), S1 (data + 16-bit address), S9 (end-of-file) |
| Line structure | Record type + byte count + 2-byte address + data bytes + 1-byte checksum (all in ASCII hex pairs) |
| First bytes | ASCII S0 (hex 53 30) - header record always appears first |
| Checksum | Ones-complement of (byte count + address + data fields), least significant byte |
| Byte order | Big-endian for address and data fields |
| Typical size | 1 KB - 2 MB (encoding overhead ~40% over raw binary; 64 KB max firmware data in S19) |
| Compression | None; firmware data is encoded as ASCII hex text with no further size reduction |
| Encryption | None; format is plain ASCII text with no security or obfuscation layer |
| Related variants | .s28 (24-bit address, S2/S8 records), .s37 (32-bit address, S3/S7 records), .srec (generic SREC) |
| Primary targets | NXP/Freescale MCU families: Kinetis, HCS08, HC12, ColdFire, HC11 |
| Released | 1970s (Motorola 6800 era) |
| Latest version | S19 is the S1/S9 variant (16-bit address, up to 64 KB); S28 (24-bit) and S37 (32-bit) are extensions |
| Open standard | Yes · royalty-free |
| Specification | en.wikipedia.org |
S19 conversions
Community Q&A
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