Chapter 23 Memory Mapping Control (S12XMMCV2)
MC9S12XDP512 Data Sheet, Rev. 2.11
910 Freescale Semiconductor
23.4.4 Chip Bus Control
The MMC controls the address buses and the data buses that interface the S12X masters (CPU, BDM and
XGATE) with the rest of the system (master buses). In addition the MMC handles all CPU read data bus
swapping operations. All internal and external resources are connected to specific target buses (see
Figure 1-26).
Figure 23-26. S12X Architecture

23.4.4.1 Master Bus Prioritization

The following rules apply when prioritizing accesses over master buses:
The CPU has priority over the BDM, unless the BDM access is stalled for more than 128 cycles.
In the later case the CPU will be stalled after finishing the current operation and the BDM will gain
access to the bus.
XGATE access to PRU registers constitutes a special case. It is always granted and stalls the CPU
and BDM for its duration.
XBus2
CPU
P0
P1
P2
P3
XFLASHXEEPROM IPBI
EBI
XBus0
ROM/REG
BDM
IO
XBus1
RAM
XRAM
2 Kbyte Registers
S12X S12X XGATE
MMC
BDM XGATE