87c521 programmer

[hwarin]

@technix : My goal is not to "use/program" a 87c521 but to dump an existing one, what have (probably) been programmed years ago in order to recover the code.

So far, to be fully complete, I've found in a garage sale a small unknown box with a PCB containing all the hardware necessary to make a Minitel external display (French ancestral videotext terminal). As it don't seems to be working, I'd like to try to dump the code in the hope that something remains readable ...

Hervé

[technix]

@technix : My goal is not to "use/program" a 87c521 but to dump an existing one, what have (probably) been programmed years ago in order to recover the code.

So far, to be fully complete, I've found in a garage sale a small unknown box with a PCB containing all the hardware necessary to make a Minitel external display (French ancestral videotext terminal). As it don't seems to be working, I'd like to try to dump the code in the hope that something remains readable ...

Hervé

Depending on the chip, your best chance might be EA hot swapping. Boot the MCU with EA pin tied LOW so it would fetch its first instructions from external bus, then raise the pin after the program counter has been placed in the external address space to bring the original EPROM contents back onto the bus so you can read and dump it.

[hwarin]

Well - I don't really see how would this trick could work.

If I start the MPU on external adress (I need a clock, of course) then it won't read any proper vector and will execute garbage, but will continue to drive the address bus. Switching back to internal address space will then execute something random from a random location and I'll never get anything.

Am I wrong ?

[technix]

Well - I don't really see how would this trick could work.

If I start the MPU on external adress (I need a clock, of course) then it won't read any proper vector and will execute garbage, but will continue to drive the address bus. Switching back to internal address space will then execute something random from a random location and I'll never get anything.

Am I wrong ?

You need to supply your EEPROM for the chip. This way it boots to your program.