PMBus™ Ancestry
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`PMBus Ancestry: PMBus and the Technologies Preceding It.
`From the beginning, power system communications have been integrated into complex systems. Power system
`communication is not a new idea. Varying levels of communication between host controllers and power subsystems have
`existed for years. In earlier times, communication allowed the power system to be monitored and enabled. Devices like power
`supply supervisors monitored the power system and communicated the power state back to system devices. When the output
`was deemed inadequate for system operation, these supervisors would hold the system in reset or notify the system of
`impending loss of power.
`
`As microcontrollers became cost effective power management devices, they were used to perform more complex control and
`monitoring of power subsystems. Initially, the control was simple on-and-off commands that could be used for sequencing. Later
`these microcontroller devices were used to control voltage outputs along with other operating parameters like current. A simple
`device like the “digipot” allowed the microcontroller to adjust the voltage sense signals and adjust current sense values.
`The digipot devices were one of many devices that take advantage of the I2C (inter-integrated circuit) bus such as memory,
`displays, sensors, and power supply ICs.
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`The I2C interface specification was created in 1982. Philips created I2C as a simple two wire interface specification suitable for
`passing data between electronic devices located on the same board or in the same chasis. In 1987, Philips was awarded US
`patent 4,689,740 for I2C. An I2C bus consists of two lines, one each for clock and data. I2C provides a means to connect multiple
`devices on a shared bus and have data representing commands, control, and information shared between a host and a
`slave device. The typical use of I2C is to have a single master device control the communication. Because of its simplicity, the I2C
`bus is widely adopted. The I2C specification has continued to be developed, allowing greater communication speeds and address
`range.
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`The I2C bus was identified as an attractive starting place as a physical communication means for industry standard specifications
`such as ACCESS.bus, SMBus, PSMI, and IPMI. The I2C interface is available on many microcontrollers; however, the simplicity also
`allows the bus to driven by software using general purpose I/O pins in many cases. For example, in 1991, a group of companies
`led the development of ACCESS.bus (or A.b), which used a version of I2C as its physical communications layer, and added two
`lines to power ACCESS.bus-enabled devices. ACCESS.bus was intended as an improved, simplified, uniform, versatile way to
`connect a computer's internal and external devices to the CPU. It could support internal devices like clocks and battery power
`monitors, and external devices like keyboards, mice, display monitors, and modems. The ACCESS.bus working group (ABIG)
`issued its last specification, version 3.0, in 1995. Several companies active in the ABIG, such as USAR Systems and Fujitsu, went on
`to become active in the Smart Battery System Interface Forum (SBS-IF).
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`Prior to 1995, battery management was accomplished through various interface methods including RS-232, one-wire, SPI, and
`I2C. There were no industry standards for either the physical interface or the command and data format. Intel and Duracell led
`development of the Smart Battery System (SBS), with the goal of implementing an industry-standard, high-level, accurate
`battery management specification that is independent of battery chemistry. The driving purpose was to make modern battery
`management available from multiple vendors while reducing the burden on the system to support multiple protocols. The
`physical protocol is the System Management Bus (SMBus) and the command language is SBD (Smart Battery Data).
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`The System Management Bus (SMBus), a version of I2C, is the physical communication layer of SBS. The upper layer of SBS issues
`commands and responses between SBS components: smart battery, smart charger, and smart selector. The commands and
`responses are transmitted using the general purpose commands of SMBus, which are mostly identical to those of I2C. These
`commands allow the battery capacity and condition to be monitored. As importantly, the SBS battery or SBS host can send
`commands to the Smart Charger to set the charger output voltage and current as well as other critical parameters. The
`resolution for the output voltage commands is in millivolts and the resolution for current is in milliamps in most cases.
`This communication interface allowed for a power subsystem to be managed and controlled so that it can perform a charger
`function that is chemistry-independent.
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`In 1996, ten promoter companies led by Intel and Duracell formed the Smart Battery System Interface Forum (SBS-IF) to maintain
`and advance the SBS and SMBus specifications. Several companies active in the SBS-IF, especially Texas Instruments, went on to
`become active in the Power Management Bus Interface Forum (PMBus-IF).
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`SBS and SMBus have become widely adopted standards in notebook computer hardware. SMBus software drivers by
`Microsoft were included in Windows starting with Windows 2000.
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`SBS and SMBus specification development ran in parallel with the creation of the Advanced Configuration and Power Interface
`(ACPI) specification (first released December 1996), in which Intel had a leading role also. ACPI was intended as the key element
`in Operating System-directed configuration and Power Management (OSPM). Implementations of SBS, and of SMBus with the
`intent to support SBS, tend to rely on ACPI-compliant systems.
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`In 1998, the SBS-IF introduced SBS 1.1 and SMBus 1.1. The main innovation in SMBus 1.1 is the introduction of an optional Packet
`Error Check (PEC) byte at the end of each SMBus communications packet. This byte is a standard 8-bit Cyclic Redundancy Check
`(CRC-8) checksum of the packet’s contents.
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`In 2000, the SBS-IF introduced SMBus 2.0, also known as SMBus on PCI. SMBus 2.0 allows device addresses to be assigned
`dynamically. The Peripheral Component Interconnect Special Interest Group (PCI SIG) then (in October 200) allocated pins 40
`and 41 on the PCI connector to SMBus clock and data respectively.
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`In 2000, the SBS-IF released its own SMBus driver for Windows. Unlike the Microsoft SMBus drivers, the SBS-IF SMBus driver could
`be used with Windows 98, and it did not rely on the presence of an embedded controller.
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`http://pmbus.org/About/PMBusAncestry
`
`5/6/2015
`Apple Inc., et al.
`Exhibit 1020
`Apple Inc., et al. v. Global Touch Solutions, Inc.
`IPR2015-01175
`
`Exhibit 1020, Page 001
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`

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`PMBus™ Ancestry
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`Page 2 of 2
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`As another example, starting in 1998, Intel introduced the IPMI (Intelligent Platform Management Interface) specification, a set of
`interfaces for OS-independent computer and cross-computer monitoring. IPMI draws on parallel Intel maintainability
`specifications such as Metolious (Metolious 1.0 was published April 1999). IPMI 1.0 uses I2C as its physical layer. IPMI 1.5 can use
`SMBus 1.1, including the optional PEC.
`
`As digitally controlled power systems are being adopted, it is apparent that there is need for an industry standard protocol for
`power communication. There are several attributes the protocol must have. The protocol must be a small burden for the
`designer, the cost, and the host. Once again an I2C-derived bus seemed to be the best compromise. SMBus has been used for
`years by SBS to manage batteries and power supplies such as chargers and backlight systems. This was considered to be a good
`place to start.
`
`So in 2004, a group of companies led the development of the Power Management Bus (PMBus), as an industry standard for power
`subsystem management. PMBus uses SMBus as its physical communication layer and includes support for the SMBus Alert as
`well as an optional Control line. The current PMBus 1.0 specification does not include address arbitration. The PMBus
`specification is divided into 2 parts: Part 1 specifies the physical layer while Part 2 specifies the command layer. In much the
`same way as SBS defines the general means to manage portable power, PMBus defines the means to manage power subsystems.
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`The PMBus initiative was endorsed by the Point-of-Load Alliance (POLA) and the Distributed-power Open Standards
`Alliance (DOSA).
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`In 2005, the Smart Battery System Interface Forum (SBS-IF), Inc., was renamed the System Management Interface Forum (SMIF),
`and reorganized to include two forums, the SBS forum (SBS-IF) and the PMBus forum (PMBus-IF). The organization took
`advantage of the symbiotic relationship of SBS and PMBus. The SBS group had been using the SMBus for nearly ten years to
`manage and control power supplies within notebook computers, so this knowledge would help the PMBus adopters in
`their development.
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`In March 2005, version 1.0 of the PMBus specification was published. The PMBus-IF has more than 30 adopter companies. It is
`through industry efforts like PMBus that new power technologies like digital power can be adopted without the need to unduly
`burden the host system with multiple protocols.
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`http://pmbus.org/About/PMBusAncestry
`
`5/6/2015
`Exhibit 1020, Page 002
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