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The MODE register cannot be written if the device is secured. So firstly ensure that the device is unsecured.
Independent of security, In normal single chip mode the MODE register is a "write once" register. This means that after each reset it can only be written to once and thereafter writes have no effect. So one possibility is that a write access has already occurred before the attempted write of 0xA0. So try applying the 0xA0 write to MODE soon after reset. If XGATE is being used, you could also check that the XGATE is not unexpectedly writing to MODE.
To ensure that internal flash is still in the memory map after the mode change the ROMON bit in the MMCCTL1 register must be set. If this is clear, then on switching to Normal Expanded Mode, the internal flash is removed from the memory map, so running code from internal flash no longer works. ROMON can be set by software or can be initialised at reset using the ROMCTL pin signal (PK7).
DPB
The MODE register cannot be written if the device is secured. So firstly ensure that the device is unsecured.
Independent of security, In normal single chip mode the MODE register is a "write once" register. This means that after each reset it can only be written to once and thereafter writes have no effect. So one possibility is that a write access has already occurred before the attempted write of 0xA0. So try applying the 0xA0 write to MODE soon after reset. If XGATE is being used, you could also check that the XGATE is not unexpectedly writing to MODE.
To ensure that internal flash is still in the memory map after the mode change the ROMON bit in the MMCCTL1 register must be set. If this is clear, then on switching to Normal Expanded Mode, the internal flash is removed from the memory map, so running code from internal flash no longer works. ROMON can be set by software or can be initialised at reset using the ROMCTL pin signal (PK7).
DPB
