--- Dennis Crawley <proyectosenpic@yahoo.com.ar> wrote:

> 
> I want to practice 8051 programming. I have a lots of boards with
> this micro and it seems it could use an external program memory 
> pulling up or down some pin. (Manual says). The micros I have seems 
> OTP, I must go to  external.

The pin is called EA (External Addressing).
> 
> Well I want to hear your suggestions, in how to make a simple
> "external" programmer. My first thought is to make a board with a pic

> :) an a flash memory. The pic receives, via RS232, the .hex and load 
> the program to the flash. Then reset the 8051.
> 
I don't recomend using a flash, you would be better off using a static
RAM with it's address and data bus preemptable from the micro
controller.  Unless the 8051 board is designed for external ROM, you'll
have a rough go of things.

1) You need to HOLD the 8051 in reset while the pic is changing the
contents of its memory. 
2) You need a clean way of decoupling the 8051 from driving the 'ROM'
memory bus. This might require the use of bus chips or a CPLD it really
depends on how you want to handle things.
3) You need to address and access the external memory. This might be
best done with an external latch to set the high order byte of the RAM
or Flash memory.  Two latches can give you 16 bits (A0 - A15) (you
could make these part of aforementioned CPLD for example).  Then you
can use a port for D0-D7 and control the read write pins from the PIC.

> My intention is to learn with a real 8051 type micro,... not virtual
> (I have at least two software simulators).
> Any clue on this I'll appreciate.
> Dennis Crawley

Good fortune!

Stephen R. Phillips


		
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