Why Can’t I Set an E5 Hardware Breakpoint in the 8051’s DATA, IDATA, or SFR Space?

The E5’s hardware breakpoint unit (BPU) monitors the Configurable System Interconnect (CSI) bus for those transactions that meet the specified breakpoint conditions.

Unfortunately, the embedded 8051’s DATA, IDATA, and non-exported SFR memory transactions bypass the CSI bus. Consequently, the E5 BPU cannot observe these transactions and cannot break on them. However, the BPU can break on exported SFR transactions because the E5’s XMAP mapper intercepts these transactions and places them on the CSI bus.

Using the Keil dScope debugger, you can set breakpoints on DATA, IDATA, or SFR space if your application executes from either internal or external RAM. Keil dScope is able to accomplish this using a software breakpoint.