MC9S12XD256CAL Datasheet, PDF (680/1348 Pages) Freescale Semiconductor, Inc – This specification describes the function of the clocks and reset generator (CRG).

Chapter 18 Memory Mapping Control (S12XMMCV3)
18.4.3 Chip Access Restrictions
18.4.3.1 Illegal XGATE Accesses
A possible access error is flagged by the MMC and signalled to XGATE under the following conditions:
• XGATE performs misaligned word (in case of load-store or opcode or vector fetch accesses).
• XGATE accesses the register space (in case of opcode or vector fetch).
• XGATE performs a write to Flash in any modes (in case of load-store access).
• XGATE performs an access to a secured Flash in expanded modes (in case of load-store or opcode
or vector fetch accesses).
• XGATE performs an access to an unimplemented area (in case of load-store or opcode or vector
fetch accesses).
• XGATE performs a write to non-XGATE region in RAM (RAM protection mechanism) (in case
of load-store access).
For further details refer to the XGATE Block Guide.
18.4.3.2 Illegal CPU Accesses
After programming the protection mechanism registers (see Figure 18-17, Figure 18-18, Figure 18-19,
and Figure 18-20) and setting the RWPE bit (see Figure 18-17) there are 3 regions recognized by the MMC
module:
1. XGATE RAM region
2. CPU RAM region
3. Shared Region (XGATE AND CPU)
If the RWPE bit is set the CPU write accesses into the XGATE RAM region are blocked. If the CPU tries
to write the XGATE RAM region the AVIF bit is set and an interrupt is generated if enabled. Furthermore
if the XGATE tries to write to outside of the XGATE RAM or shared regions and the RWPE bit is set, the
write access is suppressed and the access error will be flagged to the XGATE module (see Section 18.4.3.1,
“Illegal XGATE Accesses and the XGATE Block Guide).
The bottom address of the XGATE RAM region always starts at the lowest implemented RAM address.
The values stored in the boundary registers define the boundary addresses in 256 byte steps. The 256 byte
block selected by any of the registers is always included in the respective region. For example setting the
shared region lower boundary register (RAMSHL) to 0xC1 and the shared region upper boundary register
(RAMSHU) to 0xE0 defines the shared region from address 0x0F_C100 to address 0x0F_E0FF in the
global memory space (see Figure 18-20).
The interrupt requests generated by the MMC are listed in Table 18-22. Refer to the Device User Guide
for the related interrupt vector address and interrupt priority.
The following conditions must be satisfied to ensure correct operation of the RAM protection mechanism:
• Value stored in RAMXGU must be lower than the value stored in RAMSHL.
• Value stored RAMSHL must be lower or equal than the value stored in RAMSHU.
MC9S12XDP512 Data Sheet, Rev. 2.21
680
Freescale Semiconductor