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X1226S8 Folha de dados(PDF) 7 Page - Xicor Inc. |
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X1226S8 Folha de dados(HTML) 7 Page - Xicor Inc. |
7 / 24 page X1226 REV 1.1.24 1/13/03 Characteristics subject to change without notice. 7 of 24 www.xicor.com Table 4. Programmable Frequency Output Bits ON-CHIP OSCILLATOR COMPENSATION Digital Trimming Register (DTR) — DTR2, DTR1 and DTR0 (Non-Volatile) The digital trimming Bits DTR2, DTR1 and DTR0 adjust the number of counts per second and average the ppm error to achieve better accuracy. DTR2 is a sign bit. DTR2=0 means frequency compensation is > 0. DTR2=1 means frequency compensation is < 0. DTR1 and DTR0 are scale bits. DTR1 gives 10 ppm adjustment and DTR0 gives 20 ppm adjustment. A range from -30ppm to +30ppm can be represented by using three bits above. Table 5. Digital Trimming Registers Analog Trimming Register (ATR) (Non-volatile) Six analog trimming Bits from ATR5 to ATR0 are pro- vided to adjust the on-chip loading capacitance range. The on-chip load capacitance ranges from 3.25pF to 18.75pF. Each bit has a different weight for capaci- tance adjustment. Using a Citizen CFS-206 crystal with different ATR bit combinations provides an esti- mated ppm range from +116ppm to -37ppm to the nominal frequency compensation. The combination of digital and analog trimming can give up to +146ppm adjustment. The on-chip capacitance can be calculated as follows: CATR = [(ATR value, decimal) x 0.25pF] + 11.0pF Note that the ATR values are in two’s complement, with ATR(000000) = 11.0pF, so the entire range runs from 3.25pF to 18.75pF in 0.25pF steps. The values calculated above are typical, and total load capacitance seen by the crystal will include approxi- mately 2pF of package and board capacitance in addi- tion to the ATR value. See Application Section and Xicor’s Application Note AN154 for more information. WRITING TO THE CLOCK/CONTROL REGISTERS Changing any of the nonvolatile bits of the clock/ control register requires the following steps: – Write a 02h to the Status Register to set the Write Enable Latch (WEL). This is a volatile operation, so there is no delay after the write. (Operation pre- ceeded by a start and ended with a stop). – Write a 06h to the Status Register to set both the Register Write Enable Latch (RWEL) and the WEL bit. This is also a volatile cycle. The zeros in the data byte are required. (Operation preceeded by a start and ended with a stop). – Write one to 8 bytes to the Clock/Control Registers with the desired clock, alarm, or control data. This sequence starts with a start bit, requires a slave byte of “11011110” and an address within the CCR and is terminated by a stop bit. A write to the CCR changes EEPROM values so these initiate a nonvolatile write cycle and will take up to 10ms to complete. Writes to undefined areas have no effect. The RWEL bit is reset by the completion of a nonvolatile write cycle, so the sequence must be repeated to again initiate another change to the CCR contents. If the sequence is not completed for any reason (by send- ing an incorrect number of bits or sending a start instead of a stop, for example) the RWEL bit is not reset and the device remains in an active mode. – Writing all zeros to the status register resets both the WEL and RWEL bits. – A read operation occurring between any of the previ- ous operations will not interrupt the register write operation. FO1 FO0 Output Frequency (average of 100 samples) 0 0 Alarm IRQ output 0 1 32.768kHz 1 0 4096Hz 1 1 1Hz DTR Register Estimated frequency PPM DTR2 DTR1 DTR0 00 0 0 0 1 0 +10 0 0 1 +20 0 1 1 +30 10 0 0 1 1 0 -10 1 0 1 -20 1 1 1 -30 |
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Descrição semelhante - X1226S8 |
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