The dual-purpose RS pins are disabled by
default. The RS pins drive Low during a fallback for Master BPI configuration
mode. For initial MultiBoot systems, the RS pins are wired to upper address
bits of the flash and strapped High or Low with a pull-up or pull-down resistor, respectively.
At power-up, the system boots to the upper address space defined by the pull-up resistors on
the RS and address line connections. During a fallback, the RS pins drive Low
and the device boots from address space 0. The RS pins should be tied to
upper addresses defined by the system to allow for full bit files to be stored in each memory
segment.
Tying the RS pins to the flash upper
address pins allows for easy selection between up to four images. When using this feature with
the basic BPI asynchronous read, you should be aware that the bitstream size must be equal or
less than one fourth the size of the flash as the RS pins are held at a
static value allowing access to one fourth of the flash with one selection.