8051 Disassembler

8051 Disassembler turns a compiled Intel HEX or binary image for the 8051 and MCS-51 family back into readable assembly, then shows where every byte lives: code memory, internal RAM and the special function registers. Point it at firmware you have no source for and you can read the program, check what the compiler actually produced, or show a class what the datasheet only describes in words. It installs on Windows from the Microsoft Store or with winget, and it opens a HEX file in seconds with nothing to configure.

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Documentation

Windows: 10 (64-bit) or 11.

100% offlineyour data never leaves your machine

See exactly how your compiled program lives inside the 8051, byte by byte.

A visual way to learn, verify, and teach what the datasheet only describes.

01

Read compiled firmware as annotated assembly, not a wall of hex

Point it at an Intel HEX file and you get the program back the way the chip sees it: every byte at its address, decoded to MCS-51 assembly, with special function registers, bit addresses and interrupt vectors named instead of left as numbers. Hover any instruction to see what it does. You stop translating opcodes in your head and start reading the program. When you need it as source rather than a listing, export it to a .asm file that assembles back to the byte-identical image.
Disassembled 8051 program shown as annotated assembly beside its hex code
02

Know the file is sound before you trust a single byte

Every record is checked before anything is decoded - type, byte count and checksum - and the parsed view keeps that structure visible beside the code it carries. If an image is truncated, mis-linked or corrupted in transit you find out immediately, instead of chasing a phantom bug through a file that was never valid in the first place.
Parsed view showing each Intel HEX record with its type, byte count and checksum
03

Every interrupt vector named where it lands

The memory map labels the entry points for you - reset, external 0, timer 0, external 1, timer 1 and the serial vector - each flagged at its address with the handler sitting there. On an unfamiliar binary this is usually the fastest way in: you can see which interrupts the firmware actually uses before reading a single line of it.
Memory map with 8051 interrupt vectors labelled at their addresses

More features

04 Jump straight to an address instead of counting offsets Pick any address the image occupies from a single list and the listing moves there.
Pick any address the image occupies from a single list and the listing moves there. Vectors, entry points and every block the linker placed are already in that list, so navigating a 64 KB image is a click rather than arithmetic on a printout.
Jump to address list showing every address the loaded image occupies
05 Look up an unfamiliar opcode without leaving the app Click the info marker on any instruction and the reference opens on that exact encoding: opcode, operands, byte count, machine cycles…
Click the info marker on any instruction and the reference opens on that exact encoding: opcode, operands, byte count, machine cycles, execution time at your oscillator frequency, and which of the carry, overflow and auxiliary-carry flags it affects. No datasheet in another tab, no interrupted train of thought.
Built-in MCS-51 instruction reference showing opcode, byte count, cycles and affected flags
06 See the shape of the program, not just the listing The control flow view draws the program from its own code: entry points, subroutines, jumps, calls, returns and loops, colour-coded and…
The control flow view draws the program from its own code: entry points, subroutines, jumps, calls, returns and loops, colour-coded and navigable, with a minimap for larger images. Structure that takes an afternoon to reconstruct by hand on paper shows up as a picture in seconds.
Control flow graph of an 8051 program showing entry points, subroutines, jumps and calls
07 Keep what you work out Name any address, attach a comment to it, and save the whole thing as a project file.
Name any address, attach a comment to it, and save the whole thing as a project file. Your labels, your notes and the analysis state come back with the file, so the second session starts where the first one ended rather than from raw hex all over again. Working out what a routine does is the expensive part - this is what stops you paying for it twice.
Add label dialog assigning a name and comment to an address in the disassembly
08 Firmware past 64 KB lands where the linker put it Version 4.1 reads every record type the Intel HEX specification defines, including the extended segment and extended linear address records.
Version 4.1 reads every record type the Intel HEX specification defines, including the extended segment and extended linear address records. Images based at a non-zero segment load at their real addresses, and anything beyond the first 64 KB is shown in full rather than folded back on top of the low bank - the failure that silently corrupts a disassembly and is very hard to spot by eye.
Disassembly of an Intel HEX image spanning more than 64 KB across two banks
09 Know how much of the chip your program actually uses Occupied size counts the bytes your code really uses.
Occupied size counts the bytes your code really uses. Covered area counts everything from the lowest address to the highest, gaps included. The difference between them is the space the linker left behind - which is exactly the number you want when a part is nearly full and you are deciding whether to optimise what you have or move to a bigger device.
Occupied size and covered area statistics for a loaded 8051 program image

Supported environments.

Windows

10 (64-bit) or 11.

From people who had a deadline.

Kamlesh Narayan Engineer , GE Healthcare Verified via LinkedIn
It is a very effective tool, easy to understand and decode hex files. It saves my time.

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FREE, get it now (for Windows)

Free · direct download