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You are here: 8051 Tools Development Board Old Versions Rev 1 (1992) Schematic

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PJRC Store 8051 Dev Board, $79 LCD 20x2 Display, $11 Serial Cable, $5 12 Volt Power, $8 More Components... 8051 Tools Main Page Software PAULMON Monitor Development Board Features Photos Getting Started Example Code Memory Map Ports & Pinouts Schematic & Parts Circuit Board Construction Troubleshooting Old Versions Revision List Rev 4 (2002) Rev 3 (2001) Rev 2 (1997) Rev 1 (1992) Introduction Requirements Description Schematic Wire Wrapping Circuit Board Testing More Ideas Code Library 89C2051 Programmer Other Resources

New Rev 4 Board

A newer version (Rev 4) of this circuit board is available. Rev 4 includes a faster CPU, more memory, more I/O and an optional LCD. We recommend you use Rev 4 for new projects. We are keeping these very old pages on-line for reference to assist people who build the original version of the 8051 development board.
The very old design is difficult to troubleshoot due to the use of an external 27C64 EPROM for the monitor program. We highly recommend you use the new design for any new projects.

Schematic

Please note, pin 3 on the '138 is actually connected to ground in the printed circuit board layout instead of connected to A15 as shown here. If wire wrap construction or some other prototype technique is used to construct the board, pin 3 should be connected to A15 so that the other four address decoder lines may be used for expansion. Also, the MAX232 and its support capacitors are not included in the printed circuit board layout.

Several people have commented that the capacitor connected to pin 2 of the MAX232 chip should have it's negative terminal connected to Vcc instead of ground. Maxim's data sheet shows the typical application with it connected that way, presumably since you could use a capacitor rated for only 6.3 volts rather than 16 volts. I connect it to ground to avoid AC coupling digital switching noise from Vcc to the charge-pump supply voltage which will drive the rs-232 transmitters. The circuit will work either way, but if your capacitor is rated for only 6.3 or 10 volts, better connect is as shown in maxim's data sheet. (the cap on pin 6 still must be rated for 16 volts though) Values aren't shown, but anything between 1uF to 10uF should work fine. 0.1uF might work for baud rates under 19200.

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