Functional Description - NXP Semiconductors MC9S08SU16 Reference Manual

Functional description

28.4 Functional description
This section provides a complete functional description of the on-chip ICE system. The
DBG module is enabled by setting the DBG_C[DBGEN] bit. Enabling the module allows
the arming, triggering and storing of data in the FIFO. The DBG module is made up of
three main blocks, the comparators, trigger break control logic and the FIFO.
28.4.1 Comparator
The DBG module contains three comparators, A, B, and C. Comparator A compares the
core address bus with the address stored in the DBG_CAH and DBG_CAL registers.
Comparator B compares the core address bus with the address stored in the DBG_CBH
and DBG_CBL registers except in full mode, where it compares the data buses to the data
stored in the DBG_CBL register. Comparator C compares the core address bus with the
address stored in the DBG_CCH and DBG_CCL registers. Matches on comparators A, B,
and C are signaled to the trigger break control (TBC) block.
28.4.1.1 RWA and RWAEN in full modes
In full modes ("A And B" and "A And Not B") DBG_CAX[RWAEN and
DBG_CAX[RWA] are used to select read or write comparisons for both comparators A
and B. To select write comparisons and the write data bus in Full Modes set
DBG_CAX[RWAEN] = 1 and DBG_CAX[RWA] = 0, otherwise read comparisons and
the read data bus will be selected. The DBG_CBX[RWBEN] and DBG_CBX[RWB] bits
are not used and will be ignored in full modes.
28.4.1.2 Comparator C in loop1 capture mode
Normally comparator C is used as a third hardware breakpoint and is not involved in the
trigger logic for the on-chip ICE system. In this mode, it compares the core address bus
with the address stored in the DBG_CCX, DBG_CCH, and DBG_CCL registers.
However, in loop1 capture mode, comparator C is managed by logic in the DBG module
to track the address of the most recent change-of-flow event that was captured into the
FIFO buffer. In loop1 capture mode, comparator C is not available for use as a normal
hardware breakpoint.
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
566 NXP Semiconductors