***************************************************************************** ***************************************************************************** Buffer Issue Resolution Document (BIRD) BIRD ID#: 5.4 ISSUE TITLE: Pin Mapping for Ground Bounce Simulation REQUESTOR: Bob Ross, Interconnectix, Inc. DATE SUBMITTED: May 13, 1994, May 15, 1994 DATE ACCEPTED BY IBIS OPEN FORUM: May 20, 1995 | BIRD ID#: 5.2 | ISSUE TITLE: Pin Mapping for Ground Bounce Simulation | REQUESTOR: J. Eric Bracken, Performance Signal Integrity, Inc. and | C. Kumar, Cadence Design Systems, Inc. | DATE SUBMITTED: 6 December 1993, 17 December 1993 | DATE ACCEPTED BY IBIS OPEN FORUM: Jan 7, 1994 ****************************************************************************** ****************************************************************************** STATEMENT OF THE ISSUE: To be better able to simulate the ground bounce effect, it is necessary to know which pins of a part are connected to a common ground or power bus. This BIRD provides a simple mechanism for identifying these common buses. This improves the simulation of ground bounce by limiting the noise effects of switching drivers to other drivers and receivers on the same bus. ****************************************************************************** STATEMENT OF THE RESOLVED SPECIFICATIONS: The [Pin_Mapping] keyword is added: |=========================================================================== | Keyword: [Pin_Mapping] | Required: Optional | Description: Used to indicate which power and ground buses a given driver, | receiver, or terminator is connected. | Sub-Params: pulldown_ref, pullup_ref, gnd_clamp_ref, power_clamp_ref | Usage Rules: Each power and ground bus is given a unique name which must | not exceed 15 characters. The first column contains a pin | number. Each pin number must match one of the pin numbers | declared previously in the [Pin] section of the IBIS file. | The second column, "pulldown_ref", designates the ground bus | connections for that pin. Here the term "ground bus" can | also mean another "power bus". The third column "pullup_ref" | designates the power bus connection. The forth and fifth | columns "gnd_clamp_ref" and "power_clamp_ref" contain | entries, if needed, to specify different ground bus | and power bus connections than those previously specified. | | If the [Pin_Mapping] keyword is present, then the bus | connections for EVERY pin listed in the [Pin] section must | be given. | | Each line must contain either three or five columns. "NC" | is used for entries which are not needed or which follow | the conditions below: | | If a pin has no connection, then both the "pulldown_ref" | and "pullup_ref" entries for it will be NC. | | GND and POWER pin entries and buses are designated by | entries in either the "pulldown_ref" or "pullup_ref" columns. | There is no implied association to any column other than | through explicit designations in other pins. | | For any other type of pin, the "pulldown_ref" column contains | the power connection for the [Pulldown] table for non-ECL type | [Models]. This is also the power connection for the [GND_clamp] | table and the [Rgnd] model unless overriden by a specification | in the "gnd_clamp_ref" column. | | Also, the "pullup_ref" column contains the power connection | for the [Pullup] table and, for ECL type models, the [Pulldown] | table. This is also the power connection for the [POWER_clamp] | table and the [Rpower] model unless overriden by a specification | in the "power_clamp_ref" column. | | Column length limits are: | [Pin_Mapping] 5 characters max | pulldown_ref 15 characters max | pullup_ref 15 characters max | gnd_clamp_ref 15 characters max | power_clamp_ref 15 characters max | |---------------------------------------------------------------------------- [Pin_Mapping] pulldown_ref pullup_ref gnd_clamp_ref power_clamp_ref | 1 GNDBUS1 PWRBUS1 | Signal pins and their associated 2 GNDBUS2 PWRBUS2 | ground and power connections | 3 GNDBUS1 PWRBUS1 GNDCLMP PWRCLAMP 4 GNDBUS2 PWRBUS2 GNDCLMP PWRCLAMP 5 GNDBUS2 PWRBUS2 NC PWRCLAMP 6 GNDBUS2 PWRBUS2 GNDCLMP NC | Some possible clamping connections | ..... | are shown above for illustration | ..... | purposes | ..... 11 GNDBUS1 NC | One set of ground connnections. 12 GNDBUS1 NC | NC indicates no connection to 13 GNDBUS1 NC | power bus. | ..... 21 GNDBUS2 NC | Second set of ground connections 22 GNDBUS2 NC 23 GNDBUS2 NC | ..... 31 NC PWRBUS1 | One set of power connections. 32 NC PWRBUS1 | NC indicates no connection to 33 NC PWRBUS1 | ground bus. | ..... 41 NC PWRBUS2 | Second set of power connections 42 NC PWRBUS2 43 NC PWRBUS2 | ..... 51 GNDCLMP NC | Additional power connections 52 NC PWRCLMP | for clamps |========================================================================== General Explaination: Each power and ground bus is given a unique name which must not exceed 15 characters. An additional OPTIONAL keyword, [Pin_Mapping], is added to the specification. Following this keyword is information indicating to which power and ground buses a given driver or receiver is connected. As an example of the new format, say that we have two ground buses (named GNDBUS1 and GNDBUS2) which each bus together 3 pins: Pins: 11 12 13 21 22 23 + + + + + + | | | | | | | | | | | | Buses: +-----+------+-----> to a few +-----+------+-----> to a few GNDBUS1 drivers GNDBUS2 more and two similarly structured power buses (PWRBUS1 and PWRBUS2): Pins: 31 32 33 41 42 43 + + + + + + | | | | | | | | | | | | Buses: +-----+------+-----> to a few +-----+------+-----> to a few PWRBUS1 drivers PWRBUS2 more We assume that the "signal name" for pins 11-13 and 21-23 are all "GND", and that the names for pins 31-33 and 41-43 are all "VDD". The new [Pin_Mapping] specification would be as follows: [Pin_Mapping] pulldown_ref pullup_ref 1 GNDBUS1 PWRBUS1 2 GNDBUS2 PWRBUS2 ....... ...... ...... 11 GNDBUS1 NC 12 GNDBUS1 NC 13 GNDBUS1 NC ....... 21 GNDBUS2 NC 22 GNDBUS2 NC 23 GNDBUS2 NC ....... 31 NC PWRBUS1 32 NC PWRBUS1 33 NC PWRBUS1 ....... 41 NC PWRBUS2 42 NC PWRBUS2 43 NC PWRBUS2 Explanation: In the above example, the first column contains a pin number; each pin number must match one of the pin numbers declared previously in the [Pin] section of the IBIS file. The second column, "pulldown_ref", designates the ground bus connection for that pin; similarly, the third column, "pullup_ref", designates the power bus connection. For a GND pin, such as pins 11-13 and 21-23, the entry in the "pulldown_ref" column indicates the ground bus to which it is attached. The entry in the "pullup_ref" column is NC because there is, of course, no connection to any power bus. The situation for a POWER pin (e.g. pins 31-33 and 41-43) is analogous. The above example also contains two ordinary signal pins (pins 1 and 2). For these pins, the entries in the "pulldown_ref" and "pullup_ref" columns +designate the ground and power buses to which their buffer models are connected. Thus, for pin 1 there is an instance of the associated I-V model which connects to PWRBUS1 and GNDBUS1. Pin 2 creates an instance of an I-V model which connects to PWRBUS2 and GNDBUS2. If the [Pin_Mapping] keyword is present, then the bus connections for EVERY pin listed in the [Pin] section must be given. If a pin has no connection, then both the "pullup_ref" and "pulldown_ref" entries for it may be NC. Optional Extension: [Pin_Mapping] pulldown_ref pullup_ref gnd_clamp_ref power_clamp_ref 1 GNDBUS1 PWRBUS1 2 GNDBUS2 PWRBUS2 3 GNDBUS1 PWRBUS1 GNDCLMP PWRCLAMP 4 GNDBUS2 PWRBUS2 GNDCLMP PWRCLAMP ....... ...... ...... 11 GNDBUS1 NC 12 GNDBUS1 NC 13 GNDBUS1 NC ....... 21 GNDBUS2 NC 22 GNDBUS2 NC 23 GNDBUS2 NC ....... 31 NC PWRBUS1 32 NC PWRBUS1 33 NC PWRBUS1 ....... 41 NC PWRBUS2 42 NC PWRBUS2 43 NC PWRBUS2 ....... 51 GNDCLMP NC 52 NC PWRCLMP Explanation of Optional Extension: This extension illustrates a hypothetical situation where the clamping circuitry is connected to different rails than those of the pullup and pulldown tables. Pins 51 and 52 are hypothetical clamping supplies, and their attachments are shown at pins 3 and 4. While the nomenclature can lead to some potential confusion, the intended operation is according to this interpretation: The "pulldown_ref" column contains the power connection for the [Pulldown] table for non-ECL type [Models]. This is also the power connection for the [GND_clamp] table unless overriden by a specification in the gnd_clamp_ref column. The "pullup_ref" column contains the power connection for the [Pullup] table and for ECL type models, the [Pulldown] table. This is also the power connection for the [POWER_clamp] table unless overriden by a specification in the power_clamp_ref column. ****************************************************************************** ANALYSIS PATH/DATA THAT LED TO SPECIFICATION: One of the more serious causes of noise in digital circuits is the voltage spike created on a device's power or ground line due to the sudden switching of a very large current into that line. This can occur when other drivers share a power or ground bus with the device in question. Most modern packages incorporate many different power and ground pins and then internally connect them to several different power and ground buses. The drivers and receivers are carefully assigned to certain buses to minimize the potential impact of switching noise on the part's operation. Without a knowledge of this device-to-bus assignment, it becomes impossible to perform even a first-order simulation of the ground bounce effect. One cannot know which pins will influence any given driver or receiver. The proposed BIRD attempts to rectify this situation, while still observing an 80-character-per-line limit. ****************************************************************************** ANY OTHER BACKGROUND INFORMATION: Please note that, in order to make the simulation possible, the modelling engineer must specify the (self-)resistance and inductance for each power and ground pin in the model. The present BIRD does not address any inductive or resistive drops along the internal bus--these are assumed to be zero (the bus is treated as a perfect short between pins). Under this assumption, the equivalent impedance seen by the drivers on the bus can be found by taking the parallel combination of the series R-L impedances for each of the GND or POWER pins connected to the bus. Bird 5.2 has been issued in response to comments from the Forum members over the use of the term "NA" in Bird to indicate the lack of a connection. NA = "not available," which would have caused confusion. This version of the Bird has been updated to use "NC" (= "no connection") instead. Otherrwise, there are no changes from Bird 5.1. Reopened BIRD5.3 Background Information: BIRD5.2 is suitable as an extension to IBIS Version 1.1, but it needs some additional columns to be FULLY compatible with BIRD3 which supports up to 4 DIFFERENT Voltage References. Per the May 13, 1994 Forum and comments from Eric and Kumar, BIRD5.3 is issued. The extension consists of two additional, OPTIONAL columns for specifically designating [GND_clamp] and [POWER_clamp] connections. They will be rarely used. But in cases where the [PULLUP] is referenced to 3.3V, and the [POWER_clamp] to 5V, this extension would be useful. Also, there may need to be some clarification for ECL model types. Using BIRD5.2 as a basis and showing it completely for reference, the changes consist of "optional extension" and "explanation of optional extension" in the STATEMENT OF THE RESOLVED SPECIFICATIONS section. Two further changes are included: Per Eric's comment, I have reduced the column lengths. While 10 was suggested, I selected 15 as being a less drastic reduction while maintaining an 80 chararters per line. I do not see expansion in the number of rails, so I think this is reasonable. I agree with modifying the column names and have opted for a 3rd (compromise) choice from those selected by Kumar and Eric. The names suggested by Kumar caused the keyword line to exceed 80 characters, so I truncated the "_reference" to "_ref". I also changed "pwr" to "power" since "power" is is used throughout Version1.1 and in the proposed BIRDS. I used the underbar separation by Eric for "gnd_clamp_ref" and "power_clamp_ref". Note, while BIRD5.3 was originally intended for ground bounce simulation, it also provides the table to map external supplies connected to the pins to any [Model] within the [Component]. BIRD 5.4 was needed for specification formatting information and resolution of further details. ******************************************************************************