No voodo there, the ports are quasi-bidirectional. When configured as an input, think of "week pull-up" nothing else. I use that IC often, it is inexpensive and save me lots of I/O lines on the MCU. It has an interrupt output, which is very convenient some times. I have relocatable code for it (16f series only), if you are interested I can send it to your e-mail address. I don't post attachments here. VV John Plocher wrote: >I am starting to play with I2C and the 8574 I/O expander chip, >and I am running into some of those "I don't think I understand >the manual" types of problems. [snip] >I think I grok the cases where the chip is used as either 8 bits >of input or 8 bits of output, but I am clueless about section 7.3, >where it talks about using some pins as inputs at the same time that >other pins are used as outputs. [snip] >....but it has some voodoo that >can make it pretend to do mixed I/O if you line up various planets... --------------------------------- Do you Yahoo!? Yahoo! Finance: Get your refund fast by filing online -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body