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8051 Development Board, Rev 4

The 8051 development board provides an easy-to-use and low-cost way to develop your 8051 based microcontroller projects, without purchasing any other special equipment, such as IC programmers or emulators. All required software is available as a free download, including a C compiler!

Rev 4 Circuit Board Illustration


  • Standard 87C52 CPU clocked at 22.1184 MHz
  • 50 I/O lines!! All I/O lines are clearly labeled and available at the edge of the prototype construction area.
  • 32k SRAM, program variables and code (24k usable for code download)
  • 30k Flash ROM, non-volatile program storage and data logging
  • High speed baud rates: 115200, 75600, 38400, etc. All standard baud rates are supported (except 300 baud)
  • Display port, works with standard character-based LCDs. A 16x2 display will be available from PJRC (see photo below)
  • Eight LEDs, controlled by 8 dedicated I/O lines (not shared with the 50 I/O lines)
  • Bus expansion with 4 chip select signals, for adding UARTs, A/D converters and other bus-based peripheral chips.
  • Unregulated, polarity-protected DC voltage input with 2 position terminal block.
  • PAULMON2 monitor for easy code development without additional equipment.


  • DC Voltage, 8 to 15 volts (regulated), 50 mA or 300 mA with LCD.
  • PC Computer With Serial Port, Linux or Microsoft Windows 95-OSR2, 98, 98SE, NT4, 2000.
  • Assembler or Compiler, usually AS31 or SDCC
  • Terminal Emulation Program, eg Hyperterminal (windows), Minicom (linux)
  • Text Editor Program, eg Notepad, Vi, Emacs
  • Standard 9 pin serial cable (straight through, not null-modem!)

LCD Display Port

The 8051 development board's LCD port provides the 14 signals needed for standard character based LCD modules. A 16x2 display is available from PJRC:

Optional Display

This is a backlight display with transmissive LCD. In bright lighting (as this photo) the characters appear as highly readable green against a dark blue background. In darkness, the characters are bright green against the darker background (which does pass a small amount of the backlight, yet still remains much darker than the displayed characters). Like all character modules, eight custom (graphic) characters may be downloaded to the display, in addition to the build-in character font.

Board Photo

Revision 4 Photo

A larger copy of this photo (110k) is available for your viewing pleasure.

Demo Programs Source Code

There four programs are loaded into the flash rom memory on every assembled board as part of the testing done by PJRC. These assembly language files contain ".org" directives which place the code in Flash ROM, from F000 to F7FF. When you modify these programs, you will need to erase the originals in the Flash ROM before downloading, or change them to be built into RAM or a different location in the Flash ROM. See the memory map page for details.

This is the complete monitor code provided on the board:

  • paulmon21.asm - PAULMON 2.1 Configured For This REV 4 Board
  • extra.asm - Disassembler, Memory Editor and Single-Step Utilities
  • pm21_2f4.hex - Intel Hex For 87C52 (these two compiled and merged together)

8051 Development System Circuit Board, Rev 4, Paul Stoffregen
Last updated: February 24, 2005
Status: finished
Suggestions, comments, criticisms: <>