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INTEGRATED CIRCUITS AN10216-01 I 2 C Manual APPLICATION NOTE AN10216-01 I 2 C MANUAL Abstract – The I 2 C Manual provides a broad overview of the various serial buses, why the I 2 C bus should be considered, technical detail of the I 2 C bus and how it works, previous limitations/solutions, comparison to the SMBus, Intelligent Platform Management Interface implementations, review of the different I 2 C devices that are available and patent/royalty information. The I 2 C Manual was presented during the 3 hour TecForum at DesignCon 2003 in San Jose, CA on 27 January 2003. Jean-Marc Irazabal – I 2 C Technical Marketing Manager Steve Blozis – I 2 C International Product Manager Specialty Logic Product Line Logic Product Group Philips Semiconductors March 24, 2003 1 AN10216-01 I 2 C Manual TABLE OF CONTENTS 2 AN10216-01 I 2 C Manual 3 AN10216-01 I 2 C Manual OVERVIEW Description Philips Semiconductors developed the I 2 C bus over 20 years ago and has an extensive collection of specific use and general purpose devices. This application note was developed from the 3 hour long I 2 C Overview TecForum presentation at DesignCon 2003 in San Jose, CA on 27 January 2003 and provides a broad overview of how the I 2 C bus compares to other serial buses, how the I 2 C bus works, ways to overcome previous limitations, new uses of I 2 C such as in the Intelligent Platform Management Interface, overview of the various different categories of I 2 C devices and patent/royalty information. Full size Slides are posted as a PDF file on the Philips Logic I 2 C collateral web site as DesignCon 2003 TecForum I 2 C Bus Overview PDF file. Place holder and title slides have been removed from this application note and some slides with all text have been incorporated into the application note speaker notes. Serial Bus Overview three shared signal lines, for bit timing, data, and R/W. The selection of communicating partners is made with one separate wire for each chip. As the number of chips grows, so do the selection wires. The next stage is to use multiplexing of the selection wires and call them an address bus. IEEE1394 If there are 8 address wires we can select any one of 256 devices by using a ‘one of 256’ decoder IC. In a parallel bus system there could be 8 or 16 (or more) data wires. Taken to the next step, we can share the function of the wires between addresses and data but it starts to take quite a bit of hardware and worst is, we still have lots of wires. We can take a different approach and try to eliminate all except the data wiring itself. Then we need to multiplex the data, the selection (address), and the direction info - read/write. We need to develop relatively complex rules for that, but we save on those wires. This presentation covers buses that use only one or two data lines so that they are still attractive for sending data over reasonable distances - at least a few meters, but perhaps even km. SERIAL BUSES UART SPI B U S DesignCon 2003 TecForum I 2 C Bus Overview 5 Slide 5 General concept for Serial communications SCL SDA Typical Signaling Characteristics select 3 select 2 select 1 READ or WRITE? enable Shift Reg# enable Shift Reg# enable Shift Reg# // to Ser. // to Ser. // to Ser. R/W R/W R/W DATA “MASTER” SLAVE 1 SLAVE 2 SLAVE 3 LVTTL • A point to point communication does not require a Select control signal RS422/485 I 2 C • An asynchronous communication does not have a Clock signal I 2 C S MBu s • Data, Select and R/W signals can share the same line, depending on the protocol PECL LV PE CL LVDS I 2 C 1394 • Notice that Slave 1 cannot communicate with Slave 2 or 3 (except via the ‘master’) Only the ‘master’ can start communicating. Slaves can ‘only speak when spoken to’ GTL+ DesignCon 2003 TecForum I 2 C Bus Overview 6 CML LVT LVC 5 V 3.3 V 2.5 V GTL GTLP Slide 6 DesignCon 2003 TecForum I 2 C Bus Overview 7 Buses come in two forms, serial and parallel. The data and/or addresses can be sent over 1 wire, bit after bit, or over 8 or 32 wires at once. Always there has to be some way to share the common wiring, some rules, and some synchronization. Slide 6 shows a serial data bus with Slide 7 Devices can communicate differentially or single ended with various signal characteristics as shown in Slide 7. 4 AN10216-01 I 2 C Manual also because it may be used within the PC software as a general data path that USB drivers can use. Transmission Standards Terminology for USB: The use of older terms such as the spec version 1.1 and 2.0 is now discouraged. There is just “USB” (meaning the original 12 Mbits/sec and 1.5 Mbits/sec speeds of USB version 1.1) and Hi-Speed USB meaning the faster 480 Mbits/sec option included in spec version 2.0. Parts conforming to or capable of the 480 Mbits/sec are certified as Hi-Speed USB and will then feature the logo with the red stripe “Hi-Speed” fitted above the standard USB logo. The reason to avoid use of the new spec version 2.0 as a generic name is that this version includes all the older versions and speeds as well as the new Hi-Speed specs. So USB 2.0 compliance does NOT imply Hi-Speed (480 Mbits/sec). ICs can be compliant with USB 2.0 specifications yet only be capable of the older ‘full speed’ or 12 Mbits/sec. 2500 655 CML 400 GTLP BTL ETL 1394.a 35 10 General Purpose Logic 1 RS-422 RS-485 0.1 I 2 C RS-232 RS-423 0.5 0 10 100 1000 Backplane Length (meters) Cable Length (meters) DesignCon 2003 TecForum I 2 C Bus Overview 8 Slide 8 The various data transmission rates vs length or cable or backplane length of the different transmission standards are shown in Slide 8. Bus characteristics compared Bu s Data rat e (bits / sec) Length (meters) Length limiting f actor Nodes Typ.number Node number limiting f actor Speed of various connectivity methods (bits/sec) I 2 C 400k 2 w iring capacitance 20 400pF max I 2 C w ith buf fer 400k 100 propagation delays an y no limit I 2 C high speed 3.4M 0.5 w iring capacitance 5 100pF max CAN 1 w ire 33k 100 total capacitance 32 load resistance and transceiver current drive CAN (1 Wire) 33 kHz (typ) 5k 10km I 2 C (‘Industrial’, and SMBus) SPI CA N diff erential 125k 500 propagation delays 100 100 kHz 110 kHz (original speed) 1M 4 0 US B (low -speed, 1.1) 1.5M 3 cable specs 2 bus specs CAN (fault tolerant) 125 kHz USB (full -speed, 1.1) 1.5/12M 5 cables linking 6 nodes (5m cable node to node) bus and hub specs 25 127 I 2 C 400 kHz Hi - Sp e e d US B (2.0) 480M IEEE-1394 100 to 400M+ 72 16 hops, 4.5M each 63 6-bit address CAN (high speed) 1 MHz I 2 C ‘High Speed mode’ 3.4 MHz USB (1.1) 1.5 MHz or 12 MHz SCSI (parallel bus) 40 MHz Fast SCSI 8-80 MHz Ultra SCSI-3 18-160 MHz Firewire / IEEE1394 400 MHz DesignCon 2003 TecForum I 2 C Bus Overview 10 Hi-Speed USB (2.0) 480 MHz Slide 10 DesignCon 2003 TecForum I 2 C Bus Overview 9 Slide 9 In Slide 10 we look at three important characteristics: • Speed, or data rate • Number of devices allowed to be connected (to share the bus wires) • Total length of the wiring Increasing fast serial transmission specifications are shown in Slide 9. Proper treatment of the 480 MHz version of USB - trying to beat the emerging 400 MHz 1394a spec - that is looking to an improved ‘b’ spec - - etc is beyond the scope of this presentation. Philips is developing leading-edge components to support both USB and 1394 buses. Numbers are supposed to be realistic estimates but are based on meeting bus specifications. But rules are made to be broken! When buffered, I 2 C can be limited by wiring propagation delays but it is still possible to run much longer distances by using slower clock rates and maybe also compromising the bus rise and fall-time specifications on the buffered bus because it is not bound to conform to I 2 C specifications. Today the path forward in USB is built on “OTG” (On The Go) applications but the costs and complexity of this are probably beyond the limits of many customers. If designers are identified as designing for large international markets then please contact the USB group for additional support, particularly of Host and OTG solutions. Apologies for inclusion of the parallel SCSI bus. It is intended for comparison purposes and The figure in Slide 10 limiting I 2 C range by propagation delays is conservative and allows for published response delays in chips like older E 2 memories. Measured chip responses are typically < 700 ns and that allows for long cable delays and/or 5 [ Pobierz całość w formacie PDF ] |
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