Many thanks to all for the detective work. The page 3-34 mentioned is in a Lawrence Livermore course manual on Fundamentals of Digital Sytems Training. I love you all and will try to test you again soon. peter || | | | | | | | | Peter Van Peborgh 62 St Mary's Rise Writhlington Radstock Somerset BA3 3PD UK 01761 439 234 || | | | | | | | |