Chapter 3 Memory Mapping Control (S12XMMCV4)
MC9S12XE-Family Reference Manual , Rev. 1.19
212
Freescale Semiconductor
3.4.2.4
XGATE Memory Map Scheme
3.4.2.4.1
Expansion of the XGATE Local Address Map
The XGATE 64 Kbyte memory space allows access to internal resources only (Registers, RAM, and
FLASH). The 2 Kilobyte register address range is the same register address range as for the CPU and the
BDM module (see
XGATE can access the FLASH in single chip modes, even when the MCU is secured. In expanded modes,
XGATE can not access the FLASH when MCU is secured.
The local address of the XGATE RAM access is translated to the global RAM address range. The XGATE
shares the RAM resource with the CPU and the BDM module (see
XGATE RAM size (XGRAMSIZE) may be lower or equal to the MCU RAM size (RAMSIZE).In case of
XGATE RAM size less than 32 Kbytes (see
), the gap in the xgate local memory map will
result in an illegal RAM access (see
Section 3.4.3.1, “Illegal XGATE Accesses
)
The local address of the XGATE FLASH access is always translated to the global address 0x78_0800 -
0x78_7FFF.
is a general example of the XGATE memory map implementation.
Example 3-3.
The MCU FLASHSIZE is 64 Kbytes (0x10000) and MCU RAMSIZE is 32 Kbytes (0x8000).
The XGATE RAMSIZE is 16 Kbytes (0x4000).
The space occupied by the XGATE RAM in the global address space will be:
Bottom address: (0x10_0000 minus 0x4000) = 0x0F_C000
Top address: 0x0F_FFFF
XGATE accesses to local address range 0x0800–0x7FFF will result always in accesses to the
following FLASH block in the global address space:
Bottom address: 0x78_0800
Top address: 0x78_7FFF
The gap range in the local memory map 0x8000–0xBFFF will be translated in the global address
space:
0x0F_8000 - 0x0F_BFFF (illegal xgate access to system RAM).
Table 3-18. XGATE Implemented Memory Space
Internal Resource
$Address
XGATE RAM
XGRAM_LOW = 0x0F_0000 plus (0x1_0000 minus XGRAMSIZE)
(1)
1. XGRAMSIZE is the hexadecimal value of XGATE RAM SIZE in bytes.
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