mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 579

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

After being enabled, BDM is activated by one of the following
When BDM is activated, the CPU finishes executing the current instruction and then begins executing the
firmware in the standard BDM firmware lookup table. When BDM is activated by a breakpoint, the type
of breakpoint used determines if BDM becomes active before or after execution of the next instruction.
In active BDM, the BDM registers and standard BDM firmware lookup table are mapped to addresses
0x7FFF00 to 0x7FFFFF. BDM registers are mapped to addresses 0x7FFF00 to 0x7FFF0B. The BDM uses
these registers which are readable anytime by the BDM. However, these registers are not readable by user
programs.
15.4.3
Hardware commands are used to read and write target system memory locations and to enter active
background debug mode. Target system memory includes all memory that is accessible by the CPU such
as on-chip RAM, EEPROM, Flash EEPROM, I/O and control registers, and all external memory.
Hardware commands are executed with minimal or no CPU intervention and do not require the system to
be in active BDM for execution, although, they can still be executed in this mode. When executing a
hardware command, the BDM sub-block waits for a free bus cycle so that the background access does not
disturb the running application program. If a free cycle is not found within 128 clock cycles, the CPU is
momentarily frozen so that the BDM can steal a cycle. When the BDM finds a free cycle, the operation
does not intrude on normal CPU operation provided that it can be completed in a single cycle. However,
if an operation requires multiple cycles the CPU is frozen until the operation is complete, even though the
BDM found a free cycle.
The BDM hardware commands are listed in
The READ_BD and WRITE_BD commands allow access to the BDM register locations. These locations
are not normally in the system memory map but share addresses with the application in memory. To
distinguish between physical memory locations that share the same address, BDM memory resources are
enabled just for the READ_BD and WRITE_BD access cycle. This allows the BDM to access BDM
locations unobtrusively, even if the addresses conflict with the application memory map.
1. BDM is enabled and active immediately out of special single-chip reset.
2. This method is provided by the S12X_DBG module.
Freescale Semiconductor
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Hardware BACKGROUND command
CPU BGND instruction
External instruction tagging mechanism
Breakpoint force or tag mechanism
BDM Hardware Commands
If an attempt is made to activate BDM before being enabled, the CPU
resumes normal instruction execution after a brief delay. If BDM is not
enabled, any hardware BACKGROUND commands issued are ignored by
the BDM and the CPU is not delayed.
MC9S12XDP512 Data Sheet, Rev. 2.17
2
Table
2
NOTE
15-5.
1
Chapter 15 Background Debug Module (S12XBDMV2)
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