6522, 65C22 VIA Port +-----\__/-----+ GND |1 40| CA1 PA0 |2 39| CA2 PA1 |3 38| RS0 PA2 |4 37| RS1 PA3 |5 36| RS2 PA4 |6 35| RS3 PA5 |7 34| /RES PA6 |8 33| D0 PA7 |9 32| D1 PB0 |10 6522 31| D2 PB1 |11 30| D3 PB2 |12 29| D4 PB3 |13 28| D5 PB4 |14 27| D6 PB5 |15 26| D7 PB6 |16 25| CLK (in) PB7 |17 24| CS2 CB1 |18 23| /CS1 CB2 |19 22| R/W VCC |20 21| /IRQ +--------------+ RS0,1,2,3 are Register Select Lines. These are connected to the address bus. CLK: The CLK is an input pin. The 6522 likes to do it's own sampling of the systems clock. I am having a devil of a time finding info on this chip. However, what I did find in http://shell.ihug.co.nz/~be/6522.bug was that "the 65C22 still has a number of interrupt/timer race conditions. I don't quite remember the details of all the bugs, but I found on the order of 3 hardware bugs in the 65C22." Bfn, Bob Furber from Intec Inoventures Inc. Date: 19970916 -------------------------------------------------------------------- MC68HC16 Embedded Controllers and Software Development Tools | WebPg http://www.islandnet.com/~iii | -------------------------------------------------------------------- Intec Automation Inc. Phone 250-721-5150 | 2751 Arbutus Road Fax 721-4191 | Victoria BC V8N 5X7 | Canada | --------------------------------------------------------------------