There are better monitors around, which are of the "core" type: in the target, the code is minimized, and all the fancy tasks are performed in the host computer (PC), where the "second part" of monitor is run.

The most widespread of this type is perhaps Keil's MON51 (with the PC-countepart integrated into uVision). This has a derivative which doesn't require an external von-Neumann(isable) RAM, rather, works with self-rewriteable-("IAP"-able)-FLASH-based controllers such as the AT89C51RD2; this modification is then called FLASHMON51.

The principle was brought into almost perfection in the SST's 89x564/516, where the monitor itself sits in an extra FLASH (the boot block), hence occupies only a tiny space in the user's FLASH; and uses the same FLASH to store RAM content while running, hence it occupies only a few bytes of the stack (3, IIRC); and all this is called SoftICE. Oh yes, this chip is better known as P89V51RD2 ;-)))

JW