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Rastergraf 5.7 Talk To Me Through I2C The I2C protocol is a 2 wire serial bus originated by Philips Semiconductor. As used on the Argus, Gemini, and Sirena, the I2C devices are associated with a particular master such as a bridge. An I2C device base address is determined by a combination of device internal bits (bits 47) and (usually) three pins that are wired by the board designer (bits 1-3) Bit 0 is used to denote a Read (1) or Write (0) operation. Since most vendors combine the R/W bit with the actual I2C address (e.g. write @ 0x88, read @ 0x89), the table (below) uses that convention. The graphics boards have several 2Kbit Serial EEPROMs which can store user data and Vital Product Data (VPD) code used by Windows. An LM75 thermal sensor, placed near the center of the board on Side 1, has limit flags, interrupts, and real-time temperature read back. The LM75 must be read in 2 byte increments, otherwise it will hang the I2C bus. Table 5-4 I2C Device Addresses Device PCI6154 Primary PCI Bridge PCI6520 Primary PCI Bridge AT24C02 Borealis 2D/3D Graphics Display Monitor TH63DV164 LM75 CY22150 Reference Clock Borealis 2D/3D Graphics Display Monitor TH63DV164 CY22150 Reference Clock PCI6150 Secondary PCI Bridge AT24C02 Bt878A Video In AT24C02 Bt878A Video In AT24C02 uPD720101 USB 2.0 Host Ctrlr ISP1561 USB 2.0 Host Ctrlr AT24C02 UAC3556B USB Audio Ctrlr AT24C02 Channel Master/Slave Address R/W A A A B B B B A A B B - 5-20 Programming On-board Devices and Memories Master Master Slave Master Slave Slave Slave Slave Master Slave Slave Slave Master Slave Master Slave Master Slave Master Master Slave Master Slave 0xA9/8 0xA9/8 0x71/0 0x9D/C 0x69/8 0xA9/8 0x71/0 0x69/8 0xA9/8 0xA9/8 0xA9/8 0xA9/8 0xA9/8 Used On I2C Bus Argus/Gemini Sirena All All All All DVI All All Argus/Gemini Argus/Gemini Argus/Gemini All Argus/Gemini not used Argus/Sirena Argus/Sirena Argus Argus Argus Sirena Argus/Sirena Argus/Sirena not used 0 0 0 1 1 1 1 1 2 2 2 2 3 3 4 4 5 5 6 6 6 7 7
