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X1288S16I-2.7 bảng dữ liệu(PDF) 11 Page - Xicor Inc. |
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X1288S16I-2.7 bảng dữ liệu(HTML) 11 Page - Xicor Inc. |
11 / 31 page 11 of 31 REV 1.1.30 3/24/04 www.xicor.com Preliminary Information X1288 When used as frequency output, this signal has a fre- quency of 32.768kHz, 100Hz, 1Hz or inactive. When used as interrupt output, this signal notifies a host processor that an alarm has occurred and an action is required. It is an active LOW output. The control bits for this function are FO1 and FO0 and are found in address 0011h of the Clock Control Mem- ory map. See “Programmable Frequency Output Bits— FO1, FO0” on page 15. X1, X2 The X1 and X2 pins are the input and output, respectively, of an inverting amplifier. An external 32.768kHz quartz crystal is used with the X1288 to supply a timebase for the real time clock. The recommended crystal is a Citizen CFS206-32.768KDZF. Internal compensation circuitry is included to form a complete oscillator circuit. Care should be taken in the placement of the crystal and the layout of the circuit. Plenty of ground plane around the device and short traces to X1 and X2 are highly recommended. See Application section for more information. Figure 2. Recommended Crystal connection POWER CONTROL OPERATION The power control circuit accepts a VCC and a VBACK input. The power control circuit powers the clock from VBACK when VCC < VBACK - 0.2V. It will switch back to power the device from VCC when VCC exceeds VBACK. Figure 3. Power Control REAL TIME CLOCK OPERATION The Real Time Clock (RTC) uses an external 32.768kHz quartz crystal to maintain an accurate inter- nal representation of the 1/100 of a second, second, minute, hour, day, date, month, and year. The RTC has leap-year correction. The clock also corrects for months having fewer than 31 days and has a bit that controls 24 hour or AM/PM format. When the X1288 powers up after the loss of both VCC and VBACK, the clock will not operate until at least one byte is written to the clock register. Reading the Real Time Clock The RTC is read by initiating a Read command and specifying the address corresponding to the register of the Real Time Clock. The RTC Registers can then be read in a Sequential Read Mode. Since the clock runs continuously and a read takes a finite amount of time, there is the possibility that the clock could change during the course of a read operation. In this device, the time is latched by the read command (falling edge of the clock on the ACK bit prior to RTC data output) into a separate latch to avoid time changes during the read operation. The clock continues to run. Alarms occurring during a read are unaffected by the read operation. Writing to the Real Time Clock The time and date may be set by writing to the RTC registers. To avoid changing the current time by an uncompleted write operation, the current time value is loaded into a separate buffer at the falling edge of the clock on the ACK bit before the RTC data input bytes, the clock continues to run. The new serial input data replaces the values in the buffer. This new RTC value is loaded back into the RTC Register by a stop bit at the end of a valid write sequence. An invalid write operation aborts the time update procedure and the contents of the buffer are discarded. After a valid write operation the RTC will reflect the newly loaded data beginning with the SSEC register reset to “0” at the next sub-second update after the stop bit is written. The 1Hz frequency output from the PHZ/IRQ pin will be reset to restart after the stop bit is written. The RTC continues to update the time while an RTC register write is in progress and the RTC continues to run dur- ing any nonvolatile write sequences. A single byte may be written to the RTC without affecting the other bytes. Accuracy of the Real Time Clock The accuracy of the Real Time Clock depends on the frequency of the quartz crystal that is used as the time base for the RTC. Since the resonant frequency of a crystal is temperature dependent, the RTC performance will also be dependent upon temperature. The frequency deviation of the crystal is a function of the turnover temperature of the crystal from the crystal’s nominal X1 X2 VBACK In Voltage VCC On Off |
Số phần tương tự - X1288S16I-2.7 |
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