Methinks Kai is right. The CE is most likely used to latch the address. So why use a port pin for CE? If there are no other devices on the bus 'or' !RD and !WR together to get CE. It seems most people who post questions on this forum are trying to do shortcuts -and they don't work. There is no magic involved with microprocessors so don't expect things to work when they a fudged together.