mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 783

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

20.4.6.1
External tagging using the external TAGHI and TAGLO pins can only be used to tag S12XCPU opcodes;
tagging of XGATE code using these pins is not possible. An external tag triggers the state sequencer into
state0 when the tagged opcode reaches the execution stage of the instruction queue.
The pins operate independently, thus the state of one pin does not affect the function of the other. External
tagging is possible in emulation modes only. The presence of logic level 0 on either pin at the rising edge
of the external clock (ECLK) performs the function indicated in the
bytes of an instruction word. If a taghit occurs, a breakpoint can be generated as defined by the DBGBRK
and BDM bits in DBGC1. Each time TAGHI or TAGLO are low on the rising edge of ECLK, the old tag
is replaced by a new one.
20.4.6.2
In emulation modes a low assertion of PE5/TAGLO/MODA in the 7th or 8th bus cycle after reset enables
the unconditional tagging function, allowing immediate tagging via TAGHI/TAGLO with breakpoint to
BDM independent of the ARM, BDM and DBGBRK bits. Conversely these bits are not affected by
unconditional tagging. The unconditional tagging function remains enabled until the next reset. This
function allows an immediate entry to BDM in emulation modes before user code execution. The TAGLO
assertion must be in the 7th or 8th bus cycle following the end of reset, whereby the prior RESET pin
assertion lasts the full 192 bus cycles.
20.4.7
There are several ways to generate breakpoints to the XGATE and S12XCPU modules
20.4.7.1
The XGATE software breakpoint instruction BRK can request an S12XCPU breakpoint, via the
S12XDBG module. In this case, if the XGSBPE bit is set, the S12XDBG module immediately generates
a forced breakpoint request to the S12XCPU, the state sequencer is returned to state0 and tracing, if active,
is terminated. If configured for BEGIN trigger and tracing has not yet been triggered from another source,
the trace buffer contains no information. Breakpoint requests from the XGATE module do not depend
Freescale Semiconductor
•
•
•
•
•
Through XGATE software breakpoint requests.
From comparator channel triggers to final state.
Using software to write to the TRIG bit in the DBGC1 register.
From taghits generated using the external TAGHI and TAGLO pins.
Through the auxilliary forced breakpoint input.
Breakpoints
External Tagging using TAGHI and TAGLO
Unconditional Tagging Function
XGATE Software Breakpoints
TAGHI
MC9S12XDP512 Data Sheet, Rev. 2.17
1
1
0
0
Table 20-43. Tag Pin Function
TAGLO
1
0
1
0
Both bytes
High byte
Low byte
No tag
Tag
Table
Chapter 20 S12X Debug (S12XDBGV3) Module
20-43. It is possible to tag both
783