Code Execution from external Flash in AT89C51ED2 uC

[Thirumalesha N. (thirumalesha_n)]

Dear All,

      I'm facing issue with executing the code from external flash with 
AT89C51ED2 based controller card.

     I done EA/ pin GND while executing code from external flash.. but 
its not executing.

     Is there any other setting to do...? Bez I'm new to this 
controller.

      Your reply greatl appreciated....


Regards
Thiru N

[Peter D. (peda)]

Show us your schematic.


Peter

[Thirumalesha N. (thirumalesha_n)]

Dear Sir,

      Thank you for your valuable response

  Please find the schematic of board. My flash is "SST39SF010A-32TSOP"

 EA/ is connected to GND with 3 pin jumper(Vcc, EA, GND).

 The same schematic is working for At89S52 controller, but for 
AT89c51Ed2 its not working..

  Need to do any setting for this controller...?

   Please Reply


Regards
Thiru n

[Joerg L. (Firma: 100nF 0603 X7R) (joergl)]

Many Atmel 8051 devices have security fuses set by factory that disables 
external code execution. I have experienced this at the 89C51AC2 and AC3 
models. Took me 2 days to figure this out.

You need to use a programmer device (like the Galep4) with appropriate 
adapter and reset all (!) security fuses. This cannot be done by any 
in-circuit programming.
Datasheet explains this in only a vew very short sentences.

After doing this, my AC2 does code execution from external memory.

I assume that the ED2 device is similarily pre-programmed.
Please check datasheet.

HTH,
Joerg

[Thirumalesha N. (thirumalesha_n)]

Dear Sir,

    Ok, thank you for your suggestion,

 The data sheet says that

 "External Access Enable: EA must be externally held low to enable the
device to fetch code from external program memory locations 0000H to
FFFFH. If security level 1 is programmed, EA will be internally latched 
on
Reset."

 And also its says BLJB bit decides either boot from (BLJB = 0) boot 
loader or (BLJB = 1) application code.

   I'm not getting how to access HSB(Hardware Security Byte), in data 
sheet doesn't mentioned it.

   If you have any idea please suggest me...

Regards
Thiru N

[Joerg L. (Firma: 100nF 0603 X7R) (joergl)]

Please look at Datasheet 4235K-8051-05/08
page 95 (section 24.3.2)
Table 24-2
Security Level 4: external execution is disabled (DEFAULT)

This is exactly the same as the 89C51AC2/AC3 device.

You need a parallel programmer, because resetting these bits is not 
possible by ISP. Please read pages 94 and 95 in the Datasheet !!!

[Route_66 H. (route_66)]

Hallo!
You must the signal /PSEN combine into the chip-select-logic of the 
flash. In your schematic there are only the signals /RD and /WR 
connected to the Flash. That brings you only an external DATA-memory - 
no PROGRAM-memory.

[Thirumalesha N. (thirumalesha_n)]

Dear Sir,

     Thanks for your reply,

           Please find the schematic of control logic.

 I read the datasheet of AT89C51Ed2, it says that we can access the 
Security bytes by using APIs.. but i didn't get how to use, please 
suggest me to how to use APIs...


Regards
Thiru N

[Joerg L. (Firma: 100nF 0603 X7R) (joergl)]

Thirumalesha N. schrieb:
> ...please suggest me to how to use APIs...

Did you understand what i was writing?