Scott

Good choice on USB for true hot-pluggable interfacing but you'll have to
make a careful choice from all the available chips out there. I'm using a
Cypress part right now since it's got the features i need at an attractive
price for a full speed (12MHz) device. The original design was an "easier
to use" Anchor chip at a higher cost. ST micro has some ST7 and ST9 MCU's
for USB but i've not gone through the specs.

If you're sure you'll only need Control and Interrupt endpoints a slow
speed device should do fine. Isoch and Bulk will only work on full speed
devices so don't get caught with your pants down somewhere down the road.

Be warned that different host controllers will operate differently and the
USB specs can be a pain to understand and implement. A little birdie did
tell me there might be stand-alone host controller coming out soon and i'm
waiting to get my hands on them.


At 09:26 AM 9/20/00 -0500, you wrote:
>Has anyone used these? I've got a USB application for which these devices
may be
>well suited. I'd like to hear about any experiences others have had with
these
>chips. For example, do they work as advertised? Are there any idiosynchracies
>(like the 64 byte ram buffer is too small...)? Are they price competive?

FIFO size or double buffering shouldn't be too much of a concern for a low
speed device. You can specify the polling interval for Interrupt endpoints
from 1mS to 256mS. If you think you'll need higher bandwidth skip low speed
and go for full speed. Actual bandwidth on an unloaded bus would be about
1Mb/s and 10Mb/s total per bus.


>A little about the application:  Essentially, I'd like to interface several
>devices to one host. The devices I'm interfacing are custom (the host is
custom
>too). However, having a USB interface (or firewire or CAN or whatever)
provides
>the convenience of leveraging off existing hardware and allowing flexible
>upgrades in the future. I don't need the 480Mb/sec bandwidth in USB 2.0
and in
>fact the pic devices apparently only support the low speed of USB 1.1.
Probably
>the two most important features I seek are: low cost and ease of
implementation.
>
>Scott

I don't think USB 2.0 MCU's are available yet, only the transcievers and
SIE soft cores. Besides the low cost and ease of implementation, consider
the ease of development as well. Nothing worst then a heaping pile of
trashed OTP's or buggy development boards for a 1 way trip to the mad
house. Now where did i put my Valiums....

Terry

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