keil mon51 commands
u mean download to external ram ??... ==> Yes, uV3 will do this.
To used MON51 for debugging, you should change the MCU architecture
from Havard to von Neumann. An external SRAM is used to store user's
program. I used it for debugging several years. It could get rid of using
the ICE to debug if you can afford the cost for the ICE.
For operation theory
See
https://www.keil.com/support/man/docs/mon51/mon51_theory.htm
For download precedure
See "http://www.keil.com/support/man/docs/mon51/mon51_debug.htm"
MON51 is burned into on-chip flash or EEPROM and
is located from program address 0x0000.
So after power-on, MON51 will take control and try to
communicate with uV3 via RS-232.
(The UART on your 51 MCU is used by MON51.)
MON51 is also responsible for downloading your program to SRAM.
Your program for debugging is actually different from
the final code to release, since it can not be mapped into program
address 0x0000.
Do worry about this.
After all bugs killed, a few simple steps and just re-compile the program
will correct this.