Klaud Klaud

S12XE near RAM size?

Discussion created by Klaud Klaud on Jul 3, 2009
Latest reply on Jul 10, 2009 by Klaud Klaud

Hi all,

in the MC9S12XET512VAL we have 32 Kb RAM.

my question is how much NEAR RAM we have?


I ve searched in docs but I haven't found this information.

in AN3242.pdf I read this but I haven't understood it well:



On the S12XE, there is a new option for alternative mapping of the on-chip RAM into the 4000-7FFF fixed

memory space as an alternative to page 0xFD of the program flash. This is a write-once configuration that

allows the RAM to be configured as a 24-Kbytes flat memory map + 4-Kbytes paged (28 Kbytes flat if the

application does not page the RAM).

This is enabled by a new RAMHM bit (MMCCTL1, bit 3) and the existing ROMHM bit (MMCCTL1,

bit 1)

When both of these bits are set,

• Accesses to 0x4000–0x7FFF are mapped to 0x0F_C000-0x0F_FFFF in the global memory space

• Accesses to 0x2000-3FFF are mapped to 0x0F_A000-0x0F_BFFF in the global memory space.

The default value of the RPAGE register remains 0xFD and should be written to 0xF9 in the application

to configure a 28-Kbyte flat memory map.

Page 0xFD of the flash can be accessed via PPAGE and GPAGE instructions. By default, RAMHM is

reserved and the RAM mapping on the S12XE is fully compatible with S12XD.



Any one can help me?

thanks a lot.