Subject: Wanted...PCI bus 3V driver/receiver models

From: [email-masked] (Gary Peterson)
Date: Mon, 26 Feb 96 16:23:13 MST

I am trying to get a feel for how one might mix 3-volt level signaling and
5-volt level signaling PCI bus driver/receivers on a common PCI bus.  I have
IBIS models for 5-volt level signaling driver/receivers from the IBIS
library courtesy of Intel.  I would like to get models that are 3-volt level
signaling and "5-volt compliant" (I think this just means no VCC clamping
diode so the parts can be used with 5-volt supply) and models that are
3-volt level signaling ONLY (cannot be used with 5-volt supply because they 
have proction diodes?).

I am modeling the behavior of a specific PCI bus design using Quad XTK.  We
will run at 25MHz instead of 33MHz so have more than 10ns for data to settle.
IBIS models are preferred as they require less trouble on my part to translate
into useable Quad models (I'm one of those u-s-e-r-s who wants models that 
plug-and-play without any effort on my part...ha).  I can use Hspice models,
if that's all that is available, and will establish non-disclosure agreements 
as necessary to get them.  Thanks to any and all who are willing to help.

P.S.  I'm placing an order with ZEELAN ASAP in order to get as many
      plug-and-play models as I can afford.  I've finally bit the bullet
      and decided I'll have to pay time and $ to get the models I need.

Gary P.
---
                                  Gary D. Peterson
    _/_/_/   _/    _/  _/        SANDIA NATIONAL LABORATORIES     _/_/_/
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_/_/_/   _/    _/  _/_/_/_/  FAX: (505)844-2925             _/  _/_/  _/
                            E-Mail: [email-masked]        _/_/_/

---

From: Ben Andresen <[email-masked]>
Date: Mon, 26 Feb 1996 17:43:41 -0600

Gary, what you are requesting is in violation of PCI protocol.  There can only
be one signaling level on a PCI bus.  A universal PCI interface will have
macros that work in either 3V or 5V signaling environments, but they need to
meet all the 3V signaling specs when the PCI voltage is connected to 3V and
all the 5V specs when the PCI bus is connected to 5V.  This includes clamping
inputs to the 3V rail in the 3V signaling environment.  Anything else is non-
compliant to PCI spec.

FYI, Texas Instruments has several ASIC product lines containing universal PCI
inputs and outputs which ARE fully PCI compliant in both 3V and 5V 
environments.  If you are interested I can have our marketing department send
you additional information.

Regards,
Ben Andresen      [email-masked]

> From [email-masked] Mon Feb 26 17:27:12 1996
> To: [email-masked], [email-masked]
> Subject: Wanted...PCI bus 3V driver/receiver models
>

---

From: Arpad Muranyi <[email-masked]>
Date: Mon, 26 Feb 96 16:05:00 PST

Text item: 

Gary,

Many of the Intel chipset IBIS models have 5V safe 3.3V PCI buffers.  One 
example is the 82437VX.  To obtain some these IBIS models you might need to 
arrange an NDA agreement, but they are available.

Arpad Muranyi
Intel Corporation
============================================================================

Gary P.
---
                                  Gary D. Peterson

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Subject: Wanted...PCI bus 3V driver/receiver models
To: [email-masked], [email-masked]
From: [email-masked] (Gary Peterson)
Date: Mon, 26 Feb 96 16:23:13 MST
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---

From: Andy Ingraham <[email-masked]>
Date: Mon, 26 Feb 96 22:03:34 EST

> 5-volt level signaling PCI bus driver/receivers on a common PCI bus.

Perhaps you didn't mean to say "signaling"?  3-volt signaling and 5-volt
signaling -- as in sections 4.2.1 and 4.2.2 of the PCI spec -- are mutually
exclusive environments that can never mix.  (Like mixing TTL and ECL.)

What you can do, however, is use a device that is powered by 3.3V, and
outputs 0/3-volt output levels, on a PCI bus designated as a 5V
signaling environment.  This is what you referred to as "3-volt level
signaling and '5-volt compliant.'"

This arrangement is permitted because the output voltage specs of the
5V signaling environment are wide enough to encompass what you might
call 3V switching levels, even though they are indeed "5V signaling
environment" PCI levels.

And by the way, the output levels of these 3.3V-powered, 5V signaling
devices is rather similar to good old TTL, which, despite having 5V
power, might drive only as high as 2.4V in the high state.  The 5V PCI
switching levels are essentially TTL levels.

There are other differences besides the lack of clamping diodes that
differentiate 3.3V signaling devices from 5V signaling devices, but that
is one of the biggies.

Regards,
Andy

---

From: [email-masked] (Arthur Collard)
Date: Tue, 27 Feb 96 09:51:44 CST

> differentiate 3.3V signaling devices from 5V signaling devices, but that

  The choice Andy proposes is one which I have been working with from a
circuit rather than a model point of view. We have an automotive
customer who desires reduced system operating power while reducing
battery drain during key off. The MCU is powered by a nominal 3.3 volt
supply and interfaces with other system chips powered by 5 volts. The
IC technology for the MCU is CMOS which requires special attention to
the pin I/O driver design. First supplying switching levels from .4 to
2.4 volts is not a big problem. The problem comes in when the I/O pin
is configured as an input driven by a 5.5 volt source. The normal
configuration of a CMOS P-channel device creates a foward bias
parasitic diode from pin to the 3 volt IC rail (P-ch drain to backgate)
which will raise the IC power current limited by the 5 volt external
driving source.  There are methods to protect from this but it comes
with a cost (usually silicon area, complexity and degraded speed).
Third, the problem gets worse for advanced CMOS technologies employing
< 110 A gate oxide thickness. This implies g/d, g/s, and g/b breakdowns
close to 5.5 volts. With the advanced technology we have to protect
both N-ch pulldown and P-ch pullup from this breakdown (protect N-ch or 
P-ch - gate at Vss from drain at 5.5 volts). I have recently completed a
design of one of these 3 volt - 5 volt friendly type I/O drivers and
its not pretty but it works.

Regards

AC

 --------------------------------------------------------------------------
| M O T O R O L A  -  Advanced Microcontroller Division (AMCU)             |
| ------------------------------------------------------------------------ |
| Art Collard     Modular Circuit Design    email: [email-masked]|
| ------------------------------------------------------------------------ |
| Mail Drop: OE320                                                         |
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---

From: [email-masked]
Date: Wed, 28 Feb 96 16:13:52 EST

Gary:  I believe your situation as pictured below

             5V                       3V
              |                       |
              |                       |
           ------     PCI bus      ------ 
           | 5V  | --------------- | 3V  |
           | chip|                 | chip|
           ------                  ------  
  
is perfectly valid under the rules of the PCI protocol provided no 
additional power is drawn from the 5V when it is driving the bus.
 
FYI: Digital and others have been doing this successfully for years.  
I'll be glad to provide you with any infomation you may need for the 
success of your project. 
 
Jeff Chu
Digital Equipment Corp.
======================================================
======================================================
Date:	26-FEB-1996 18:55:05.73
From:	CRL::"[email-masked]" "Gary Peterson"
Subj:	Wanted...PCI bus 3V driver/receiver models
To:	[email-masked], [email-masked]
CC:
I am trying to get a feel for how one might mix 3-volt level signaling 
and
5-volt level signaling PCI bus driver/receivers on a common PCI bus.  I 
have
IBIS models for 5-volt level signaling driver/receivers from the IBIS
library courtesy of Intel.  I would like to get models that are 3-volt 
level
signaling and "5-volt compliant" (I think this just means no VCC 
clamping
diode so the parts can be used with 5-volt supply) and models that are
3-volt level signaling ONLY (cannot be used with 5-volt supply because 
they 
have proction diodes?).

I am modeling the behavior of a specific PCI bus design using Quad XTK.  
We
will run at 25MHz instead of 33MHz so have more than 10ns for data to 
settle.
IBIS models are preferred as they require less trouble on my part to 
translate
into useable Quad models (I'm one of those u-s-e-r-s who wants models 
that 
plug-and-play without any effort on my part...ha).  I can use Hspice 
models,
if that's all that is available, and will establish non-disclosure 
agreements 
as necessary to get them.  Thanks to any and all who are willing to 
help.

Gary P.
---
                                  Gary D. Peterson
    _/_/_/   _/    _/  _/        SANDIA NATIONAL LABORATORIES     _/_/_/
   _/       _/_/  _/  _/        P.O. Box 5800, M/S 0503            _/_/
  _/_/_/   _/ _/ _/  _/        Albuquerque, NM 87185-0503     
_/_/_/_/_/_/
     _/   _/  _/_/  _/        Phone: (505)844-6980           _/  _/_/  
_/
_/_/_/   _/    _/  _/_/_/_/  FAX: (505)844-2925             _/  _/_/  _/
                            E-Mail: [email-masked]        _/_/_/

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% From: [email-masked] (Gary Peterson)
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% To: [email-masked], [email-masked]
% Subject: Wanted...PCI bus 3V driver/receiver models

---

From: Scott McMorrow <[email-masked]>
Date: Wed, 28 Feb 96 15:02:00 PST

Text item: 

> differentiate 3.3V signaling devices from 5V signaling devices, but that

In a 5 volt signaling environment with 3.3V voltage level devices, you may want 
to be careful about low to high switching of the 3.3 V devices on the bus.  5 
volt devices will overshoot far enough to turn on the high clamp diodes, 
supressing the ringback component to reasonable levels.  But with 3.3 volt 
drivers, all of the overshoot energy will ringback and can enter the threshold 
region of receivers on the PCI bus.  With small geometry, fast devices, there 
can be an extreme amount of overshoot.

--scott

Scott McMorrow

[email-masked]

Cc: [email-masked]
Subject: Re: Wanted...PCI bus 3V driver/receiver models
To: [email-masked], [email-masked], [email-masked]
From: [email-masked] (Arthur Collard)
Date: Tue, 27 Feb 96 09:51:44 CST
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---

From: Ben Andresen <[email-masked]>
Date: Wed, 28 Feb 1996 17:32:33 -0600

Jeff, I agree that 5V chips powered from 5V and 3V chips powered from 3V can
both talk on a PCI bus, but it isn't as simple as you show it to be.  The
motherboard defines the signaling environment, EITHER 3V or 5V.  All cards
must meet the specs for that signaling environment, and the characteristics
are different.  The 3V signaling environment input thresholds are much tighter
than for 5V so an input buffer conforming only to 5V specs will not be 3V PCI
compliant.  The output buffer V-I characteristics change between 3V and 5V
operation.  Also, there MUST be a Vcc clamp diode for 3V PCI (PCI Local Bus
Spec Rev 2.1, section 4.2.2.2) which will cause outputs driving 5V rail to 
rail severe problems in a 3V signaling environment.

Bottom line is you must use I/Os specifically designed for the signaling 
environment defined by the motherboard to be PCI compliant.  You CAN'T 
arbitrarily mix 3V and 5V signaling components and expect it to work.  This
doesn't say anything about the supply voltages and technologies of the 
various components on the bus which can be almost anything.  I'm talking only
about the PCI signaling environment as defined by the motherboard.

If the final signaling environment is undefined the solution is to use
"universal" PCI I/O buffers.  These sense the PCI signaling environment being
used by measuring the PCI I/O designated power pin voltage, and adapt their 
characteristics to fit the appropriate specs.  These CAN be used as without
reservation as described in your msg below.

Ben Andresen  

> From [email-masked] Wed Feb 28 15:23:37 1996
> To: [email-masked]
> Cc: [email-masked], [email-masked]
> Subject: RE:Wanted...PCI bus 3V driver/receiver models
>