Chapter 3 Memory Mapping Control (S12XMMCV4)
MC9S12XE-Family Reference Manual , Rev. 1.19
218
Freescale Semiconductor
Figure 3-23. MMC Block Diagram
3.4.4.1
Master Bus Prioritization regarding access conflicts on Target Buses
The arbitration scheme allows only one master to be connected to a target at any given time. The following
rules apply when prioritizing accesses from different masters to the same target bus:
•
CPU always has priority over BDM and XGATE.
•
XGATE access to PRU registers constitutes a special case. It is always granted and stalls the CPU
for its duration.
•
XGATE has priority over BDM.
•
BDM has priority over CPU and XGATE when its access is stalled for more than 128 cycles. In the
later case the suspect master will be stalled after finishing the current operation and the BDM will
gain access to the bus.
•
In emulation modes all internal accesses are visible on the external bus as well and the external bus
is used during access to the PRU registers.
3.5
Initialization/Application Information
3.5.1
CALL and RTC Instructions
CALL and RTC instructions are uninterruptable CPU instructions that automate page switching in the
program page window. The CALL instruction is similar to the JSR instruction, but the subroutine that is
IPBI
FLASH
CPU
BDM
EEE
EBI
MMC “Crossbar Switch”
XSRAM
XGATE
BDM
FTM
S12X1
S12X0
XGATE
XBUS3
XBUS0
XBUS1
XRAM
XBUS2
BLKX
DBG
resources
FLEXRAY
S12X2
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