Vybrid GPIO Boot override

[rod_k]

In the TWR schematics, I see that the RCONxx (GPIO Boot override) lines are "driven" with active IC buffer devices at POR. Is this required, or can the lines be simply pulled up or down with appropriate resistors? I know the manual has a ton of info, but I can't find (yet) what the status of these GPIO lines are at POR...? High-Z?  Basically my question refers to all the lines, including: - BOOT_MODE[1:0]... selects the boot mode - RCON5, 6, and 7... selects the boot device - all the other RCON lines that have particular meaning for a given boot mode and device... Can we just use resistors or do we need active devices with drive capability? Thank you.

[naoumgitnik · Accepted solution]

Dear Rod,

The lines of interest are shared – used for the RCON function during the processor reset state and for other functions / peripherals afterwards; if you can guarantee that outputs of these peripherals are in the High-Z state while the RCON states are read by the processor, you may use resistors only.

There is no such guarantee in the modular “Tower” approach, therefore transparency buffer ICs controlled by the same reset signal as the processor itself are used – their powerful outputs override any interference on these lines when the RCON values are read but switch to the High-Z state when the processor is released from reset.

Sincerely yours, Naoum Gitnik.