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PAULMON2 Hardware Requirements
This system isn't very useful... you can't download programs because there is no external RAM chip, but this system will "boot-up" and PAULMON2 will run properly. If a programmable 8051 family chip (8751, 87C51, 87C52, 89C51, 89C52, etc) is available, and a prototype construction technique (wire wrap, point-to-point, etc) is used, it is easiest to build and test this minimal system first, and then add the external RAM and other components after the minimal system is working.
Of course, the 8752 chip must be programmed with PAULMON2, so a programmer which can write to the 8752 is needed to initally program it.
Useful SystemTo build a useful system, at least one external RAM chip is required so that code (other than PAULMON2 itself) can be run. At least two more chips are required, as shown here:
This schematic simply connectes the two chip select pins to the A13 and A15 lines, which causes the 8k of memory to appear in two locations, 0x2000 to 0x3FFF, and 0x6000 to 0x7FFF.
Because no additional I/O hardware is provided, programs written to run on this board will only be able to do I/O using the serial port. Most applications will require additional aditional I/O hardware, but this minimal useful system can be used to test simple programs which communicate via the serial port.
Compatible ProcessorsNearly all 8051 compatible processors will with the PAULMON2. Many 8051 type processors contain special hardware, which PAULMON2 will not use, but can be used by programs which are downloaded and run using the monitor.
Serial Port InterfaceThe schematics above show the MAX232 chip interfacing between the 8051 and a PC's serial port. Other chips such as the 1488/1489 can be used, but for a prototype board the "5 volt only" feature of the MAX232 (and equivilant chips) is a good idea, since it is more difficult to make wiring errors which can destroy the chips on the board if only a single +5 volt power supply is used.
RAM and Memory MappingPAULMON2 does not require RAM to run, but programs can not be downloaded unless RAM (or Flash ROM) is present to hold the downloaded data. Standard versions of PAULMON2 expect ram to located at 0x2000, 0x4000, or 0x8000. Within the PAULMON code are LJMP instructions which cause interrupts to jump to the associated locations in RAM (e.g. 0x0003 jumps to 0x2003 for the INT0 interrupt). It is possible to configure PAULMON2 for RAM located in other places.
To be useful, the RAM must be connected so that it can be read as code memory. In other words, the PSEN line must be able to select a read from the RAM.
Flash ROMPAULMON2 can support Flash ROM. PAULMON2 was designed and tested with the AMD 28F256 Flash ROM chip. Large chips may be used, though they will contain more memory than the available 64k address space of the 8051, so only a portion may be used. AMD offers a newer 28F256A chip, which has a simpler programming interface. PAULMON2 has not been tested with this chip. The 29Fxxx series chips are not supported at this time.