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Looking for a CPU

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patroclus

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Hi,

I'm trying to find a microprocessor for building a small system that is able to execute code from external memory. In microcontroller world, I used PIC in asm, and ARM7 in C, and I also know a bit on AVR. Even thouhg ARM7 rules, all of them have an internal flash rom for code, with I/O pins, but not proper address and data buses, at least those from atmel and philips.

Anyone could help me?

Thanks
 
so you want a processor, with built in ram (or rom?), but you still want full access to the address bus and data bus? :confused:

I don't know of such a thing?
 
I don't need an internal sram or rom.
A Z80 could do the job, but not at 10 or 20 MHz... I need something more close to ARM7's 50 MIPS... I can't believe there're no CPUs like this...

Of course, I can't go for something serious like an Intel Pentium, Athlon, or PowerPC, neither chips that are expensive for a hobbyist project...
I don't know the VIA CPUs, I might check them out...
 
Some of the high end PIC18s has external memory capability. They are cheap and easy to find. You can give it a try. :)
 
I want to execute code from removable and interchangeable memories, because there will be different things the same system can do... it's like an old computer, or an old-videogame console, which required cartridges.

The SD idea is cool. I already thought about it. But, as far as I know, it should copy the code to sram, and run from there, which lowers flexibility. Anyway, along with a Z80, these two are my best candidates.

The PIC18 with full address and data buses? I'll check it out too, but I don't remember anything like that (I'd bet not, really, but I'll be cautious).
 
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patroclus said:
I want to execute code from removable and interchangeable memories, because there will be different things the same system can do... it's like an old computer, or an old-videogame console, which required cartridges.

The SD idea is cool. I already thought about it. But, as far as I know, it should copy the code to sram, and run from there, which lowers flexibility.
There's nothing stopping you having a bootloader run at first boot that checks an SD card for new firmware and flashes it into the chip before running that code. You could do this easily with any of the later flash PICs and no doubt other processors like the ARM7.

The PIC18 with full address and data buses? I'll check it out too, but I don't remember anything like that (I'd bet not, really, but I'll be cautious).
There are indeed such chips! They are in the PIC 18F series and I remember them being TQFP
 
aussiepoof said:
There are indeed such chips! They are in the PIC 18F series and I remember them being TQFP
Well the ARM7 is not exactly dip either :)

If you can still find an old PIC17 series those had external RAM/ROM
 
As it's a new project, I'd rather use a chip which is in production and not deprecated, like Z80, maybe rabbit, or I might probably go for an ARM7 like LPC or atmel's, and use a bootloader to flash with new firmware, or copy blocks and run from sram...
 
patroclus said:
As it's a new project, I'd rather use a chip which is in production and not deprecated, like Z80, maybe rabbit, or I might probably go for an ARM7 like LPC or atmel's, and use a bootloader to flash with new firmware, or copy blocks and run from sram...
My primary reason for suggesting the bootloader/flash approach is that most (if not all) modern uC's have a *lot* more flash that SRAM! On the PIC you can't run code from SRAM... and the bootloader/flash approach allows you to write much larger programs.

Just my 2c ($AU)
P.
 
I found LPC22xx series, which have an external memory interface, with full data and address buses. Also some Atmel's, both ARM7 based.

I don't know about LPC, but I heard good things about them, I guess I will have to check the dev tools and software before going for the LPC or Atmel ones. From Atmel I know the tools for AVR, which are quite great, and free.
 
patroclus said:
I want to execute code from removable and interchangeable memories, because there will be different things the same system can do... it's like an old computer, or an old-videogame console, which required cartridges.

It really depends EXACTLY what you're trying to do, there's no need to have interchangeable memory in a ROM pack, you could have a micro-controller in a plug-in pack instead - which would be considerably cheaper, presuming your applications can fit in their available memory.

For that matter, you don't even need to have the same micro-controllers in the packs. you could have different ones for different purposes, just using a common interface for the plug-in.

But, like I said, it really depends on what you're trying to do, and the available space - but a simple PIC will make a Z80's performance look really sick.
 
That's a good idea, but I'm trying to build a stand alone system, which connects
to a TV, and allows to swap code from one application to another. I want to make
it a general purpose small and portable system.
As I want to use the same microcontroller to generate the burst signals for the
TV by software, to send it via composite cable, I need quite a fast chip.
At least 20 MIPS.
That's why I rather have an ARM7 with an external memory or SD card interface, than
spending that amount of money everytime I need a new application. Small flash
memory like 29F040 is much cheaper and so big for this things.
 
Sure.
Yes, I want the microcontroller to generate a video signal, so you can actually make applications that are displayed in a TV.
For that purpose, I thought of using some D/A converters, or just a simple resistor ladder, for luma (brightness), and a pulse generator with variable phase (maybe using different inverters to add delays) for chroma. This is my first projects that involves TV signals, and I only have theory knowledge.
 
patroclus said:
Sure.
Yes, I want the microcontroller to generate a video signal, so you can actually make applications that are displayed in a TV.
For that purpose, I thought of using some D/A converters, or just a simple resistor ladder, for luma (brightness), and a pulse generator with variable phase (maybe using different inverters to add delays) for chroma. This is my first projects that involves TV signals, and I only have theory knowledge.

Perhaps you should study how it's been done historically, and how it's been done in more modern times?. Generating the chroma signal in software doesn't sound a good idea, or a very practical proposition.
 
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