Searching \ for '[EE]: USB interface question' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=usb+interface+question
Search entire site for: 'USB interface question'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: USB interface question'
2001\11\30@024849 by Bob Barr

flavicon
face
I'm about to do my first USB interfacing with a 16C745 and need some
clarification on the best way to connect it up. My questions
specifically relate to the USB6B1 ESD protection chip. (Those JW '745
chips are expensive so I thought I'd better ask rather than popping
one accidentally.)

Cypress's schematic shows a USB6B1 chip between the USB connector and
their EZ-USB micro. There are also two 22 ohm series resistors (one
each in the D+ line and the D- line) between the USB6B1 chip and the
EZ-USB chip.

Is any of this necessary when connecting USB to the 16C745? I haven't
yet found a schematic for the Microchip USB demo board (Does one
exist?) so I can't tell if I'm looking for trouble or not.

If it's a good idea to use the USB6B1 even with the '745, there are a
few things I find confusing about the data sheet. Any help would be
appreciated.

The USB6B1's data sheet shows Vbus, D+, D- and GND on pins 1 through 4
being passed straight through to pins 8 through 5 of the chip. Four
diodes are shown between the lines (clamping D+ and D- between Vbus
and ground). There is also a 'Transil' diode (zener) between Vbus and
ground.
On the first page of the datasheet, the connector is shown hooked to
pins 5 though 8. On the second page, the connector is shown hooked to
pins 1 through 4. Since the lines go through the chip, is there any
reason to prefer one direction over the other? It wouldn't appear to
make any difference.

Are the 22 ohm resistors needed? They're not referenced in the
datasheet at all.

Thanks, Bob

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\30@132217 by Marc Reinig

flavicon
face
Definitely put the 22 Ohm resistors in.

In terms of the USB6B1,  it is meant to protect your device up to 8KV.  If
you want to market your device in Europe, it's probably necessary.  But for
general use, the ~2KV protection of the chip itself is sufficient.

Marc Reinig
System Solutions


{Original Message removed}

2001\11\30@153804 by Andrew Warren

flavicon
face
Bob Barr <spam_OUTPICLISTTakeThisOuTspammitvma.mit.edu> wrote:

> I'm about to do my first USB interfacing with a 16C745
> ....
> Cypress's schematic shows a USB6B1 chip between the USB connector
> and their EZ-USB micro. There are also two 22 ohm series resistors
> (one each in the D+ line and the D- line) between the USB6B1 chip
> and the EZ-USB chip.
>
> Is any of this necessary when connecting USB to the 16C745? I
> haven't yet found a schematic for the Microchip USB demo board
> (Does one exist?) so I can't tell if I'm looking for trouble or
> not.

   Bob:

   I assume that you're referring to the Cypress EZ-USB Development
   Kit schematic.  We include the ESD protection chip on that board
   because it's likely to be used in an environment that'll expose
   it to lots of ESD.  In products that don't have that exposure, it
   can be omitted and you can rely on the 2-3KV ESD protection
   provided by the EZ-USB chip itself.  I would expect the PIC
   inputs to have about the same level of protection as the EZ-USB
   chips.

   The 22-ohm resistors are for impedance matching.  Cypress's
   oldest EZ-USB chips require those external resistors, but all
   the newer ones incorporate them into the chip.  The PIC16C745
   requires external resistors.

   I'm glad to see that our documentation is helping you design your
   product, even if you ARE using Microchip microcontrollers
   instead of our (cheaper, faster, better) parts.

   -Andy


=== Andrew Warren -- .....aiwKILLspamspam@spam@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\30@161703 by Bob Barr

flavicon
face
On Fri, 30 Nov 2001 11:13:45 -0800, you wrote:

>
>    I assume that you're referring to the Cypress EZ-USB Development
>    Kit schematic.  We include the ESD protection chip on that board
>    because it's likely to be used in an environment that'll expose
>    it to lots of ESD.  In products that don't have that exposure, it
>    can be omitted and you can rely on the 2-3KV ESD protection
>    provided by the EZ-USB chip itself.  I would expect the PIC
>    inputs to have about the same level of protection as the EZ-USB
>    chips.
>

Actually, I'm using the docs for another USB development board as a
guide. Sorry, I've forgotten the link right off-hand but *it* is
probably based on Cypress's design. I'm primarily a bit-twiddler with
a pretty good hardware background (more at the tech level than the
design level). I try to provide a heads-up to the hardware guy I'm
working with whenever I can.

>    The 22-ohm resistors are for impedance matching.  Cypress's
>    oldest EZ-USB chips require those external resistors, but all
>    the newer ones incorporate them into the chip.  The PIC16C745
>    requires external resistors.

The 16C745/765 datasheet (DS41124C) shows D+ and D- connected directly
to the micro.
I finally got the PICDEM-USB User's Guide (DS41174A). Microchip's site
has a bad link on the 'download' button for it but the 'view' button
works. There are no external resistors shown in their schematic.

Did I perhaps miss an errata sheet somewhere?

>
>    I'm glad to see that our documentation is helping you design your
>    product, even if you ARE using Microchip microcontrollers
>    instead of our (cheaper, faster, better) parts.
>

At this point, I'm pretty much locked in to the Microchip parts but
I've certainly got my eyes open for any opportunity to use the Cypress
EZ-USB in the future. It certainly looks like one sweet piece of
silicon. :=)

Regards, Bob

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2001\11\30@163253 by David VanHorn

flavicon
face
Does anyone have a correct app note with the schematic surrounding the
FT232AM chip?
The one on their web site has pinouts that don't match the chip data sheet
at all, and is missing most of the schematic itself.
(or maybe I didn't find the "good " one yet..)
--
Dave's Engineering Page: http://www.dvanhorn.org

Got a need to read Bar codes?  http://www.barcodechip.com
Bi-directional read of UPC-A, UPC-E, EAN-8, EAN-13, JAN, and Bookland, with
two or five digit supplemental codes, in an 8 pin chip, with NO external parts.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...