Software simulator for MCS51

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Simulator is available for two platforms: DOS and UNIX but DOS version is not supported any more. DOS version is not finished so I call it demo version and it is available in binary only. Limitations of DOS version are:

There is no built in help available;
Some of the utilities are not working, for example calculator, bit simulator;
Serial line works in mode 1 independently of mode bits.

I used this simulator to verify my applications and I never used missing feautres mentioned above, so I think that this "demo" version can be usefull anyway.

UNIX version is under development, 0.1 version is the first one which works.

MCS51 Simulator for DOS: s51.zip 164k
MCS51 Simulator for UNIX: s51-0.2.0.tar.gz 162k (included these pages in doc directory)

How to install

DOS version

Get the ZIP file and unzip it. ZIP file contains three files: s51.exe the executable itself, dpmi16bi.ovl and rtm.exe. Last two files are required because s51.exe is a DOS protected mode program. Put these files in a directory which is in the PATH or keep them together with the s51.exe.

UNIX version

UNIX version is distributed in source.

Get archive file, uncompress and untar it. These steps will produce a directory s51-X.Y.Z where X.Y.Z is the version number.
Go to the directory and configure the package. Issue configure command. It will determine your system and make Makefile. Istallation directory can be specified with --prefix=dir option to the configure. Default directory is /usr/local. Executable file will be placed in bin subdirectory.
Compile the package with make command.
Install executable s51 to any directory you want. It can be done with make install command which will place files in installation directory specified with --prefix=dir option of configure. Note that you may have to have special privilege to do this if installation directory is not writable by you.

How to use

DOS version

S51 for DOS has written in Borland Pascal using Turbo Vision to produce menu driven, multiwindow user interface which is very easy to use. The program can be started using following command:

C:\> s51 [input file]

Parameter is optional. If it specified it must be the name of an Intel hex file. Some screenshots of the program and short descriptions of them:

UNIX version

The simulator can be started in the following way:

$ s51 [-hHVvP] [-p prompt] [-t CPU] [-X freq[k|M]] [-c file] [-s file] [files...]

Specified files must be names of Intel hex files. Simulator loads them in specified order into the ROM of the simulated system.

Options:

-t CPU

Type of CPU. Recognized types are: 51, 8051, 8751, C51, 80C51, 87C51, 31, 8031, C31, 80C31, 52, 8052, 8752, C52, 80C52, 87C52, 32, 8032, C32, 80C32, 251, C251. Note that recongition of a CPU type as option does not mean that the simulator can simulate that kind of CPU. Default type is C51.

-X freq[k|M]

XTAL frequency is freq Hertz. k or M can be used to specify frequency in kHZ or MHz. Space is not allowed between the number and the k or M. Default value is 11059200 Hz.

-c file

Open command console on file. Command consoles is on standard input and output by default. Using this option the console can be opened on any file for example on the serial interface of the computer.

-s file

Connect serial interface of the simulated microcontroller to the file. Nothing is used by default which means that characters transmitted by serial interface of the simulated microcontroller go to nowhere and it will never receive anything. If you are going to communicate with serial interface interactively the best idea is to specify a teminal with -s option.

-p prompt

Using this option you can specify any string to be the prompt of command interpreter, for example:

$ s51 -p "s51> "
Software Simulator of MCS51, version 0.0.1
s51>

-P

Prompt will be a null ('\0') character. This feature can be usefull for programs which controlls simulator through a pipe.

-V

Verbose mode. The simulator notifies you about some kind of internal actions for example interrupts. Messages are printed on command console.

-v

Print out version number and stop.

-H

Print out types of known CPUs. Names printed out by this option can be used to determine CPU type using -t option.

-h

Print out a short help about the options and stop.

The simulator can be controlled with a simple monitor program which uses the command console to read commands and print out results. After starting the program you see a prompt on the command console and you can write in commands after the prompt:

$ s51
S51 0.2.0, Copyright (C) 1997 Daniel Drotos, Talker Bt.
S51 comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
> h
l file             Load (intel hexa) file
dl,do              Download (intel hex) data
g [start [stop]]   Go
pc [address]       Get/set content of PC
s [step]           Step
n [step]           Next
bs f|d addr [hit]  Set FETCH Breakpoint
bse wi|ri|wx|rx|ws|rs|rc f|d addr [hit]
                   Set EVENT Breakpoint
bd addr            Delete FETCH Breakpoint
bde wi|ri|wx|rx|ws|rs|rc addr
                   Delete EVENT Breakpoint
ba                 Delete all breakpoints
bl                 List Breakpoints
dis [start [offset [lines]]]
                   Disassemble code
dc [start [stop]]  Dump code in disass form
dch [start [stop]] Dump code in hex form
di [start [stop]]  Dump Internal RAM
dx [start [stop]]  Dump External RAM
dr                 Dump registers
dp                 Dump ports
ds [addr...]       Dump SFR
db addr...         Dump bit
si addr data...    Set Internal RAM
sx addr data...    Set External RAM
sc addr data...    Set code (ROM)
ss addr data...    Set SFR area
sb addr data...    Set bit
sp port data       Set port pins
fi start stop data Fill IRAM area with `data'
fx start stop data Fill XRAM area with `data'
fs start stop data Fill SFR area with `data'
fc start stop data Fill ROM area with `data'
res                Reset
wi,Wi string       Search for `string' in IRAM (Wi case sensitive)
wx,Wx string       Search for `string' in XRAM (Wx case sensitive)
wc,Wc string       Search for `string' in ROM (Wc case sensitive)
sopt opt value     Set value of option
gopt [opt]         Get value of option(s)
q                  Quit
show c|w           Show licensing information
h,?                Help about commands
>

In command reference you can find more information about breakpoints and execution of the simulated program.

Code analyzer

This feature is included into both DOS and UNIX versions. Code analyzer analyzes the code of the simulated program and tries to figure out which address contains valid instruction. Analyzer starts analyzing of the code with address 0 which always must contain an instruction because reset of the device sets zero into program counter. So, analyzer marks address 0 that it contains an instruction. Then it marks the address of the next instruction and so on. If the analyzer finds a jump instruction it continues with destination address of the jump instruction. If it finds a call instruction, it recursively analyzes destination address as well as next instruction follows the call one. Analyzator stops if it finds an address which is already marked or if it finds a return instruction or an indirect jump which is impossible to follow. All these mean that it is impossible to discover all instructions of the program.

This problem is solved in very simple way in UNIX version. If the execution reaches an umarked address, the analyzer is called to analyze the code starting at actual address pointed by the PC. This method is not included into DOS version but this re-analyzation can be requested by pressing Ctrl-F7 at any time.