Hello! A long since closed shop in Manhattan sold me a collection of items wearing legends for the Atari families of hardware. One such was the MMU for the computers that company made. Running the part number of CO61618 through Google sent me off to a website that presented me with the information regarding what it did. I sent them back a note that the part was in fact a HAL16L8 part, and started off as 99 PAL16L8, (I found out years earlier that after the first 100 part numbers ordered, the company could commision a mask for making them up that way.), any this site, https://www.atarimax.com/jindroush.atari.org/achip.html provided all of the other information needed to ID the other parts. Except they did not help me to elucidate what the terms on the MMU meant. One of them was the use of PB0 and PB1. Now I know of those from the SY6522 IO chip for the SY6502 CPU. Would one of you who is more familiar with the way the Atari computers work know if they were using an SY6522 that way? ----- Gregg C Levine gregg.drwho8@gmail.com "This signature fought the Time Wars, time and again."