S12XDP512 CHIP MODES (144 pin)

[sfb]

Hi,

I will use S12XDP512 with normal expanded mode (attached external RAM but program memory is internal flash). I want to know that am I right:

I can do mode selection in two ways, first during reset pin active (low) by hardware pull up BKGD- MODC, pull down PE6-MODB pull up PE5-MODA and pull up PK7-ROMCTL. Second way is setup this bits by software in MODE register.

So if I do this settings from software by MODE register I can use this pins (except BKGD) for general purpose I/O.

[kef]

Not at all. Yes, you can switch for example from single chip mode to expanded mode manipulating MODE register bits. You can use MODA and MODB pins for I/O in both modes, but these two pins are sampled by MCU to determine the initial mode. You won't be happy if your external hardware will pull MODx pins so that you land in illegal modes MODC:MODB:MODA = 1:1:0 or 1:1:1.

So MODx pins I/O is somawhat limited. It's safer to use MODx pins only for Output. But you still should make sure there are no large caps on MODx pins.

And using MODx for input is somewhat very dangerous since external device has to sense MCU /RESET pin, and when your external device senses /RESET = low, it should reset used MODx pins to the state valid for mode your MCU should operate in...