ISD51 User's Guide
ISD51 (In-System Debugger) is a small debug monitor (500-700 bytes) that links with your 8051 target program. It interfaces to the µVision Debugger using the 8051's on-chip UART and allows you to view memory, set breakpoints, single-step, and perform numerous debugging operations.
ISD51 is royalty-free and may be included with your end-product for field-level software debugging and monitoring. You software is safe from unauthorized debugger access since the original source code is required for debugging.