Hi, I was wondering what size of internal RAM does P89C668 have? all 8051 processors have 128 bytes plus 128 bytes of SFR. I have read that some 8051 microcontrollers have an additional memory block of 128 locations to be use in parallel to SFR. this additional memory is accessed using indirect register addressing. how can i know if this additional memory does exist in a micrcontroller as micrcontroller datasheets seem hard to get? can i rely on the assembler IDE and use "indirect addressing" on any address between 80 and FF? if the assembler accepts my instruction this means that the micrcontroller has this embedded memory. Cheers