On 9/22/06, peter green wrote: > why can't you just implement spi on the fpga? > Oh I need to have many isolated channels and I can not afford the space and cost of an FPGA every channel. In can however afford an FPGA to process these many channels of data in the other side of the opto isolation. I could have used SPI directly. However I am facing a practial limitation that SPI simply requires too many optocouplers. This sound a bit crazy, I know... Regards, Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist