Adding USB Interface to Low-Cost 8-Bit Microcontroller

An off the shelf solution:

have many other solutions at:

Cheers Don...

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The Microchip USB PICs are quite easy to use. It should be possible to reflash the application via the USB connection.

Leon

My guess is that your only cost-effective way to get USB is going to be to replace the current micro with one that has USB. Even really simple dedicated USB chips like USBserial tend to internally be mask- programmed first-generation USB-enabled 8051 parts. So basically, by adding a second part you are putting two micros in the system; probably going to be cheaper to find one that does both jobs.

Might it be acceptable for cutomers to have to buy a special cable to do it? If so, this could be a cheap USB-serial cable. This would avoid the cost overhead of adding USB just for updates.

Lots.. you'll probably want to consolidate it on one controller, as others have mentioned. Freescale probably has the most mature USB support, but you can find many others (Microchip, etc.). It's even possible that some 32-bit ARM variants are cost-competitive. Best regards, Spehro Pefhany

We'd like to avoid customers purchasing a special cable, but that approach may be preferable to carrying the cost of a special chip in every product. Thanks for the suggestion.

When you say USB-serial cable, which of these were you referring to:

a)A cable with effectively no active components (if this exists, I've never seen it), OR

b)A USB-serial converter, which normally has a little circuit board and some active stuff in it somewhere, i.e.

I'm assuming (b), but if (a) exists I'd be grateful to know about it.

Thanks, Dave A.

One with the circuitry shoved int he connector.

Of course you will also need a level translator in your project. Unless you can find and specify a cable with logic level output. Or, if you want to be sneaky, that can reliably accept logic level input from your device, and you play some game with passives to let your device handle RS232 input levels from the cable. And I think you have to remember to invert the signal someplace.

At this late date I'm just adding my vote, but...

If I were in a hurry, or if my design team really didn't seem up to learning how to do the USB thing, then I'd consider one product rev with an FTDI chip or similar, talking serial to the other micro. It would probably be easier to implement the secure boot code, and it would give you a chance to learn half the problem then half again, but you'd spend a lot of money on the production floor.

Probably, I'd end up going to the microprocessors that include USB. There are plenty of inexpensive 8-bitters out there, so you should have a wide range to choose from. Your production volumes are high, so you can (or at least should be) able to afford the time to make it work. Heck, if your volumes are high enough you should be able to arm-twist the processor vendor into making it all work for you, and you'll just have to put it in.

Many cheap USB-serial cables only do +5V/0V output. Even for proper ones you only need a resistor.

b)

Don...

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MAX3240 seems like a good option. I'm planig to use in a project. It comes with a evaluation board to start with.

Thanushan

Others have already directly answered your question so I'm not going to. However, are you sure that you really need USB? You seem to have gone from requirements to that conclusion in a single bound so I can't help suspecting maybe there is a little tunnel vision here.

Many flash memory card formats have integral SPI interfaces - Secure Digital comes to mind. Since you already have an SPI interface you can add SD support to the hardware with little more than adding a connector assembly and making whatever modifications are necessary to the PCB and case. USB card readers are cheap - SD readers are under a fiver retail here in the UK, and that cost and the cost of the card itself are only necessary if the customer wishes to upgrade

- I suspect that will be a minority for most consumer devices.

Of course, you will need software on your device to read the card and reprogram the device accordingly, but you will need some software however you go, and that software will almost certainly be simpler than adding USB support. The software will be greatly simplified if you can dump your new flash image to the card as a raw device, rather than needing to deal with a filesystem layer.

"David T. Ashley" skrev i meddelandet news:yaqdnfLQ1Z1-SNDVnZ2dnUVZ snipped-for-privacy@giganews.com...

If you want to make this as simple as possible for the user, then you could implement a boot monitor with USB - CDC on your target. When such a device is connected to the USB bus a COM port appears on the PC, and you can use any application communicating over a serial port to send data to the target. Hyperterminal with X-Modem should always be available on a Windows PC.

The target should have USB and selfprogramming capability.

There are several AVR/AVR32/AT91SAM7 (ARM) circuits meeting those requirements.

If you do not mind the customers getting their own cable, then the AVR-ISP Mk II will let you reprogram the device using a 6 pin header using the SPI port. This will allow you to use cheaper parts, because they will not need USB, nor selfprogramming. The cable is $36 at Digikey

Andrew Smallshaw schrieb:

Another approach might be to use "good old" RS232 - it's the cheapest standard interface you can have with a small micro.

Those who want to do program updates either need a PC that still has an RS232 interface, or use one of the uncountable USB-RS232 converters that are around (and cheaper than you can implement an USB interface).

You don't have to care about all the USB stuff, and a simple serial protocol is easily implemented on any micro.

Tilmann

Having used the FTDI devices, may I respectfully suggest the MAXIM parts? MAX3420 for USB peripheral only, or MAX3421 for host and peripheral modes.