Well,

The 8051 devides the clock supplied to it on its XTAL source pins by 12 to get the onchip clock frequency. So, a 12MHz crystal reveals a 1MHz clock source - no problem for an 8255 to handle.

Secondly, YES Richard, i have a -5 part on the board, so again no problem. As far as the textbooks are concerned, please can any one name one textbook at freshman level that tells its students to us Lattice or Xilinx CPLDs or FPGAS with an 8052 to expand its IO structure, that also memory mapped style ?

Common texts include "The 8051 Micrcontroller" by Scott Mackenzie, 2) The 8051 Micrcontroller and Embedded Systems by Muhammad Mazidi, 3) The Intel Microprocessors by Barrey B. Brey (Latest editions), etc..

I can name more than 18 books on the subject, and not one book deviates from mentioning the 8255 and its use and connections with the 8052, less mentioning CPLDs or FPGAs or GALs. The only book even mentioning GALs and PALs is the Intel microprocessor book and that also for memory address decoding - nothing else.

The two 8051 books mentioned here also contain a schematic diagram of a SBC and a monitor program. This is a very simple SBC, and hence the urge and inspiration for a high density SBC was felt. Hence, i started designing this project.


So guys, i know we are all abreast of technology, maybe you guys are more than i am due to our geographic disparate locations, but a freshman is a freshman without any such boundaries. And they all have to start from somewhere, in this case, its the past that they have to adopt in teh present to understand the HOW THINGS WORK phenomenon, so they can move on to more advanced topics.