Hi Forum Members,
I need your help. My product is still in the design phase. So I will
explain the product requirement and then the queries.

My design Need:
1. The Booting of the product must be from Internal ROM, where I initialize some
peripherals. I do not want the lower level programmers to have access to this
section of code (for my program security also).
2. The lower level programmers can be programmers from my office or from my
customer's office.
3. My Internal initialization program may be of the size ranging from a few tens of bytes
to about 20 kbytes. It will depend upon the customer specifications.
4. I am designing a product using P89C51RD2HBP (because it is easily available here).

I am exploring the possiblity, whether I can put the user
program code in external EPROM begining at (external Program) address 0x1000,
and my Bootup code in Internal Program Memory starting at address 0x0000.
After power on reset the CPU will jump to my program in IROM,
My code will do some basic initializations, and give the control to the external
program (external EPROM) either by call or jump to those locations.

My questions are:
1. Can this design work ? If yes, Can you give the details about implementing this?
2. Can this be achieved by connecting a port pin of CPU through an inverter to EA pin.
So that CPU starts my IROM program after POR. And my IROM Program does some basic
initializations, changes the state of this control pin, and give a jump to 0x1000 ?
I know I might have to put the "ljmp 0x1000" (in the external Program memory)
at the next location where my master program ends.
Is it possible ?
3. Datasheets talk about EA pin is used for boot up from external or internal ROM,
It also says that this pin is latched during POR, and is in-effective for any changes
on this pin later.

4. I am suggesting step 2, because, I know of certain people, who can copy the
Internal Program of ICs having fired Program Security bits. If they can do it,
then there is a possibility of EA having some function after POR.
Then there might be a possiblility of Step 2. Has anybody tried this ?



Kiran V. Sutar.

Note : POR = Power On Reset.
IROM = Internal Program Memory.