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W149 Datasheet(PDF) 5 Page - SpectraLinear Inc |
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W149 Datasheet(HTML) 5 Page - SpectraLinear Inc |
5 / 15 page W149 Rev 1.0, November 21, 2006 Page 5 of 15 Serial Data Interface The W149 features a two-pin, serial data interface that can be used to configure internal register settings that control particular device functions. Upon power-up, the W149 initializes with default register settings, therefore the use of this serial data interface is optional. The serial interface is write-only (to the clock chip) and is the dedicated function of device pins SDATA and SCLOCK. In motherboard applica- tions, SDATA and SCLOCK are typically driven by two logic outputs of the chipset. Clock device register changes are normally made upon system initialization, if any are required. The interface can also be used during system operation for power management functions. Table 3 summarizes the control functions of the serial data interface. Operation Data is written to the W149 in eleven bytes of eight bits each. Bytes are written in the order shown in Table 4. Table 3. Serial Data Interface Control Functions Summary Control Function Description Common Application Clock Output Disable Any individual clock output(s) can be disabled. Disabled outputs are actively held LOW. Unused outputs are disabled to reduce EMI and system power. Examples are clock outputs to unused PCI slots. CPU Clock Frequency Selection Provides CPU/PCI frequency selections through software. Frequency is changed in a smooth and controlled fashion. For alternate microprocessors and power management options. Smooth frequency transition allows CPU frequency change under normal system operation. Output Three-state Puts clock output into a high-impedance state. Production PCB testing. (Reserved) Reserved function for future device revision or production device testing. No user application. Register bit must be written as 0. Table 4. Byte Writing Sequence Byte Sequence Byte Name Bit Sequence Byte Description 1 Slave Address 11010010 Commands the W149 to accept the bits in Data Bytes 0–6 for internal register configuration. Since other devices may exist on the same common serial data bus, it is necessary to have a specific slave address for each potential receiver. The slave receiver address for the W149 is 11010010. Register setting will not be made if the Slave Address is not correct (or is for an alternate slave receiver). 2 Command Code Don’t Care Unused by the W149, therefore bit values are ignored (“Don’t Care”). This byte must be included in the data write sequence to maintain proper byte allocation. The Command Code Byte is part of the standard serial communication protocol and may be used when writing to another addressed slave receiver on the serial data bus. 3 Byte Count Don’t Care Unused by the W149, therefore bit values are ignored (“Don’t Care”). This byte must be included in the data write sequence to maintain proper byte allocation. The Byte Count Byte is part of the standard serial communication protocol and may be used when writing to another addressed slave receiver on the serial data bus. 4 Data Byte 0 Refer to Table 5 The data bits in Data Bytes 0–7 set internal W149 registers that control device operation. The data bits are only accepted when the Address Byte bit sequence is 11010010, as noted above. For description of bit control functions, refer to Table 5, Data Byte Serial Configuration Map. 5 Data Byte 1 6 Data Byte 2 7 Data Byte 3 8 Data Byte 4 9 Data Byte 5 10 Data Byte 6 11 Data Byte 7 |
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