Changes
Port F8FFh is a documented, but rarely known I/O address, used by the standard BIOS functions MC_BOOT_PROGRAM and MC_START_PROGRAM (vector BD13h and BD16h). These functions are usually executed when starting a binary program with RUN"FILENAME.BIN", both functions do issue an "OUT [F8FFh],FFh". This feature is intended to allow Peripherals to re-initialize themselves when needed. From the official [[SOFT158]] specs:
:"All expansion peripherals should be reset when an output is performed to I/O channel #F8FF. In particular a peripheral that generates interrupts must not generate an interrupt until it is re-initialised after such an output has been performed."
Most or all peripherals (including Amstrad's own [[DDI-1]]) aren't following that suggestion, and usually there is no need to do so. There may be a few special cases there hardware could take use of it, such like interrupt generating devices, especially if they do access formerly allocated memory.
