BUS_PORT aka the memory mapped $B5xx addresses W/ CS'

[teejsd]

 I would like to use this external device expansion BUS_PORT as it is called in the various manuals that I have for the MC68HC11.  The problem is, I can't find any hard data on how to do so!  My most pressing question is, do I need to set the direction of the data pins (D0-7) everytime before I write to my address block, and if so, how/where?

 Do I need to use the R/W pin that's on that bus? (if so, how?)  And, if I write all my addresses for my external device to the same CS' address block, is the CS' going to pulse every time I change address?  Anybody found an AppNote on this, because I sure didn't and it wasn't for lack of trying.....TJ

[jimw]

Are you refering to the Port expander device or just interfacing external memory to the hc11?  I think that was the 68hc24. I never worked with it. I used methods like used on the handyboard and others.

Here is a manual for a replacement. Tekmos claims its an exact replacement for the 68hc24.

http://www.tekmos.com/standard_products/TK68HC24_Part.PDF

Memory mapped IO can be done without a port expander.

Here is a schematic for the handyboard that uses external memory and port expansion without the PRU http://www.handyboard.com/schemv12/cpu.gif