USB-Serial adapter giving fits.

linuxguy

Well, I seem to be yet another user having problems with USB-rs232 adapters.

Instead, I did read the forums, and found that this is due to a handshaking issue.

Why exactly does the BS2 require handshaking? According to the HomeWorkBoard spec sheet, it uses a PIC16C57. I've used a few programmers, and none of them required handshaking.

What makes your equipment special in that requires these rs232 commands?

Chris Savage

Hello,

The DTR line resets the Stamp Module to prepare for identification or programming. The timing of that line is important. It’s not always the handshaking lines, some of the USB to Serial adapters have poorly written drivers which cause other timing issues. It would seem the problem is with many of the USB to Serial adapters. We have a known compatible adapter for under $20.00 at the following link. I hope this helps. Take care.

http://www.parallax.com/detail.asp?product_id=28031

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Chris Savage
Parallax Tech Support

linuxguy

Thanks for the reply.

I've seen these problems before, over at the guy who sells the Garmin serial connecters, and with really crummy laptops.

The Garmin parts guy www.pfranc.com recommends USB-serial connections via MCT part # U232-P9. Figuring that I do tentatively trust his word, I opened my Belkin F5U109 usb-serial connector.

I find a U232-P9 as the main processor in there... Something fishy.

I also have used this connector in flashing circuits that required specific timings, along with other various hardware-hacking like things (hackaday.com is a good example of this). What I do find strange is that the PIC programmers dont require this.

Forgive me if I sound skeptical, but I am.

allanlane5

Well, actually, ALL "PIC" programmers require SOME 'handshaking', in order to use the PIC 'native programming' mode. That you haven't seen it just means it's happening 'under the covers'.

Now, the BS2 programming algorithm was designed some time in the 1990's, when everybody had 'native' serial ports on their computers. At the time, using DTR for an 'Attention!' signal to the BS2, to interrupt whatever the BS2 was doing and tell it to prepare to be programmed, was a clever way to go about it.

Now, in these days when many laptops don't even come with floppy drives, let alone serial ports, you need a simple USB to Serial adapter to enable you to use the BS2. Well, some vendors (Belkin especially) 'cut corners' with their USB adapters, so that while their TX and RX work fine, they don't implement exact timing for the "RS232 hardware handshake signals" (RTS, CTS, DTR). This is a problem with Belkin, not Parallax.

Parallax HAS recommended an inexpensive USB to Serial adapter that they KNOW works. And there's nothing intrinsically wrong with their programming algorithm "handshake". So I think Parallax has done all they can do to get around this issue.

Note I myself do tend toward the skeptical side of things, but Parallax has proven themselves to me over time. My above explanation comes from 2 years or so experience using Parallax products. And in that entire time, I've found Parallax products to be some of the most reliable, robust, well documented, and simple to use of the PIC industry.