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I am using the cypress an2125 with the 8051 core. I am trying to receive data on the 8051 data bus (Port D) from an external source. Whenever the external source initializes to an output, the cypress chip goes into an unknown state. Is there some way to initialize Port D as an input, or disable some interrupt that may be occurring?
D0-D7 are active only for external bus accesses. However they are driven low during suspend. If the Wr, Rw, FRd, FWr pins are not set up as IO's, look to see if any of them are active. Maybe you are doing some hidden bus accesses. Make sure the part does not go into suspend unless the the external sources are tristated.