8051/8031 series MCU replace/upgrade ROM issues ?

my 8031 board is essentially a romless 8051 (minus program memory as datasheet says) .

the board has an external ROM chip for 8031 to read.

can one sub an 8051 with on chip ROM that is null **with out worries** my concern would be the 8051 on chip ROM conflicting with the external ROM ???

and of course how likely to copy external ROM to the 8051 on chip rom and loose external ROM witout any code mods ????

I have not digested enough about how the ROM usage occurs to figure it out ... yet

some guidance would be appreciatted, robb

Reply to
robb
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On a standard 8051, the /EA pin controls whether program code is fetched from an external ROM (/EA is pulled low) or whether the program code is fetched from the internal ROM (/EA is pulled high, and the program address being fetched is within the address range of the internal ROM).

On your board, /EA is probably hardwired to ground. If you substitute an 8751, or a masked-ROM part, and don't change the wiring of /EA to ground, the new chip will fetch code from the external ROM just as the current chip does.

You should be able to load the ROM contents, program it into an EPROM or OTP or flash-based 80x1's internal program memory, re-wire the /EA pin (connect it to Vcc rather than to ground), and run the code with without needing an external ROM. If the specific chip you use is otherwise hardware-compatible with the one you are replacing, I'd expect that no code changes at all would be needed.

--
Dave Platt                                    AE6EO
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Reply to
Dave Platt

Exactly. Notice that the processor needsa hard reset to switch between memory models. You can't switch between internal or external ROM with your i/o etc. It needs a hard reset.

Pieter

Reply to
Pieter

is

high, and

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great ! yes, the /EA (pin 31) is tied to ground through a 4.7k resistor just as you proposed

chip

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ah great news. I am trying to repair the microcontroler board and at times during the repair process i wonder if i should try and improve or simplify (of course there is the issue of adding more unknown factors) but if it helps reduce the number of components and appears an obvious improvement then why not try ...

Thanks for the help and info, robb

Reply to
robb

is

high, and

of the

should there be any circuit pre-cautions to wiring /EA to Vcc ?

should i wire direct to closest Vcc source or should i put some component combo between Vcc and /EA ?

thanks again fo the help, robb

Reply to
robb

I'd treat it like any other I/O pin. If CMOS, you can probably wire it directly to Vcc. If TTL, I'd use a series 4k7 resistor to protect it against a possible voltage spike on the Vcc rail.

Since your board already has such a resistor tying /EA to ground, I'd consider just lifting the grounded end of that resistor and jumpering it to Vcc.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
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Reply to
Dave Platt

If you're being paid to repair it, just make it work per the print, using as close to OEM parts as you can get.

If you're being paid to modify it, raise your rates. ;-)

Good Luck! Rich

Reply to
Rich Grise

Vcc ?

some

wire

ground, I'd

jumpering

Thanks for your time and help Dave,

do you happwn to have idea of cheapest/simplest way to get ROM data in and out of the 8051 ?

i see a variety of devices such as Evaluatoin boards, dev boards, serial adapters, serial programmers, downloaders and program burners ? quite a variety of prices and sophistication or equipment.

i just want to be able to copy code to and from 8051 not neccesarily to develop any applications if the best option incleudes those features then ok but it is not the intention .

thanks again, robb

Reply to
robb

It depends very much on the specific type of chip.

If I recall correctly, classic 8751 parts were/are EPROM-based, and require a programming algorithm much like a standard EPROM - a relatively high programming voltage, repeated programming pulses, and so forth. A "real" device programmer is usually needed for this sort of part, and a UV EPROM eraser is needed to blank the device and make it available for programming.

Some newer 80C51-type processors have a much-easier-to-work-with programming architecture - 5-volt-only, often designed for in-circuit programming with just two or three pins using a serial programming algorithm. I think that some such parts can be programmed using just a PC's parallel port and a handful of simple components, well within the scope of almost any electronics hobbyist.

You'll need to select the microprocessor chip you're planning to use before you can decide on a programming methodology.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
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Reply to
Dave Platt

I've found some inexpensive programmers on ebay. e.g.

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And many of the modern flash memory based parts can be programmed in circuit.

Graham

Reply to
Eeyore

ROM

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programmed in circuit.

Thanks graham,

I just bought a xeltek universal programmer for $5 (us) on ebay .. just waiting for delivery. i do not really have my expectations set too high though.

i mainly asked the question to defer to you experts and experienced peoples as to which equipoment is best suited for my task.... which is reading old 23256 and/or 8051 ROMs and then writting to newer 27c256 ROMS or 8051 ROM space.

Ebay is littered with junk and few gems and i was hoping someone could give me an idea of a gem to seek. then i can wait and watch

thanks , robb

Reply to
robb

Right. You need a programmer with MCU capability to do that.

Graham

Reply to
Eeyore

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