MC3S12RG128 Datasheet, PDF (201/546 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 7
Breakpoint Module (BKPV1) Block Description
7.1 Introduction
This block guide describes the functionality of the Breakpoint (BKP) sub-block of the HCS12 Core
Platform.
The Breakpoint contains three main sub-blocks:
• Register Block
• Compare Block
• Control Block
The Register Block consists of the eight registers that make up the Breakpoint register space. The Compare
Block performs all required address and data signal comparisons. The Control Block generates the signals
for the CPU for the tag high, tag low, force SWI, and force BDM functions. In addition, it generates the
register read and write signals and the comparator block enable signals.
NOTE
There is a two-cycle latency for address compares and for forces, a
two-cycle latency for write data compares, and a three-cycle latency for read
data compares.
The Breakpoint sub-block of the Core Platform provides for hardware breakpoints that are used to debug
software on the CPU by comparing actual address and data values to predetermine data in setup registers.
A successful comparison will place the CPU in Background Debug Mode or initiate a software interrupt
(SWI). The choice between Background Debug Mode and SWI is software selectable.
There are two types of breakpoints, forced and tagged. Forced breakpoints occur at the next instruction
boundary if a match occurs and tagged breakpoints allow for breaking just before a specific instruction
executes. Tagged breakpoints will only occur on addresses of program fetches. Tagging on data is not
allowed; however, if this occurs nothing will happen within the BKP.
The range function of the BKP allows breaking within a 256-byte address range. The page function allows
breaking within expanded memory. In data matching operations, 8-bit or 16-bit data can be matched.
Forced breakpoints are mainly used on a read or a write cycle, but can be used on any bus cycle.
MC3S12RG128 Data Sheet, Rev. 1.05
Freescale Semiconductor
201