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AD9546/PCBZ データシート(PDF) 158 Page - Analog Devices |
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AD9546/PCBZ データシート(HTML) 158 Page - Analog Devices |
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158 / 205 page  AD9546 Data Sheet Rev. 0 | Page 158 of 205 USER TIME STAMP PROCESSOR 0 (UTSP 0) REFERENCE TDCS DIGITAL CROSS POINT MUX CLOCK SOURCE (DERIVED FROM SYSTEM CLOCK) USER TIME STAMP SOURCE 0 TIME STAMPS AUXILIARY NCOS USER TIME STAMP PROCESSOR 1 (UTSP 1) USER TIME STAMP SOURCE 1 AUX NCO 0 TIME SCALE AUXILIARY REFERENCE TDCS DPLL FEEDBACK TDCS LOCAL TIME SCALE INVERSE USER TIME STAMPERS (IUTS) 8 80 REG 0x3A1D TO 0x3A14, BITS[79:0] REG 0x3A2B, BIT 0 REFERENCE TIME SCALE FOR UTSP 1 80 80 80 80 LOCAL TIME SCALE REFERENCE TIME SCALE FOR UTSP 0 80 80 80 80 AUX NCO 1 TIME SCALE AUX NCO 0 TIME SCALE AUX NCO 1 TIME SCALE AUX NCO 0 TIME SCALE AUX NCO 1 TIME SCALE TIME STAMP SOURCES NOTE 1. A RANGE OF BITS USES A COLON SEPARATOR TIME STAMPS TIME STAMPS TIME STAMPS TIME STAMPS REG 0x3A29 TO 0x3A20, BITS[79:0] REG 0x3A2A, BITS[7:0] REG 0x300F, BIT 3 REG 0x2A13, BITS[7:6] REG 0x3A1F, BIT 0 REG 0x3A1E, BITS[7:0] REG 0x300F, BIT 2 8 80 REG 0x2A13, BIT 5 REG 0x2A12, BIT 5 REG 0x2A12, BITS[4:0] REG 0x2A12, BITS[7:6] REG 0x2A13, BITS[4:0] Figure 107. User Time Stamp Processors INTERPRETING USER TIME STAMPS The outputs of the UTSPs comprise 80-bit words with the least significant bit weighted as 2−40. The units associated with a time stamp converted by a UTSP depends on the selected time scale. Specifically, the 80-bit user time stamp consists of a 40-bit integer part (the 40 leftmost bits) and a 40-bit fractional part (the 40 rightmost bits), as shown in Figure 108. Each count of the integer part represents one period of the selected time scale. The 40 fractional bits represent the fractional part of one period of the selected time scale with a resolution of 2−40. 0 79 40 39 ... ... 80-BIT USER TIME STAMP 2–40 INTEGER PART FRACTIONAL PART DECIMAL POINT Figure 108. User Time Stamp For example, assume the 80-bit word is the hexadecimal number, 0x 0000 0000 B10E 04F0 07C1, in which case the decimal equivalent is 194,673,770,497,985. Because the scale of the fractional part is 2−40, the time stamp value (rounded to 10 decimal places) is Time Stamp Value = 194,673,770,497,985 × 2−40 = 177.05476284207634307676926255226 = 177.0547628421 This time stamp value represents periods of the selected time scale. For example, suppose the selected time scale is auxiliary NCO 0, which the user had programmed with a frequency of 10052.630025 Hz (corresponding to a period of 99.476455167760936272992897696939 μs). Thus, the time associated with the example time stamp (177.0547628421) is the time stamp value multiplied by the period of selected time scale (99.476455167760936272992897696939 μs), which is 0.017612780178 sec (rounded to the nearest ps). That is, the time stamp in this example indicates a time of approximately 17.6 ms. Time stamps have a meaningful resolution of approximately 1 ps. Thus, digits in a time stamp calculation representing less than 1 ps must be ignored. In a digitized clocking application, the AD9546 produces a local time scale. Because the local time scale advances at a rate commensurate with external time keeping (rather than based on periods of a programmed frequency as with the auxiliary NCOs), the local time scale is better suited for relating time stamps to external time. |
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