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CDP1879 Datasheet(PDF) 8 Page - Intersil Corporation |
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CDP1879 Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 18 page 4-111 Operational Sequence Power is applied and the real-time clock is reset. This sets the interrupt output pin high. After the CS pin is set high and with address 7 on the address input lines, the control register is loaded via the data bus to configure the clock. With selective addressing, the seconds through month counters are then written to and loaded to set the current time. The real-time clock will now hold the current “wall clock” time, with an accuracy determined by the crystal or external clock used. If the alarm function is desired, the control register is accessed and loaded again. This new byte will allow subse- quent time data to be entered into the seconds, minutes and hours alarm latches. This sequence is also used when select- ing one of the 15 available clock-out signals. If the alarm function was selected, the interrupt output pin will be set low when the values in the seconds, minutes and hour alarm latches match those in the seconds, minutes and hour counters. If one of the 15 sub second-to-day clock outputs is selected by the byte in the control register, the clock output pin tog- gles at that frequency (50% duty cycle) The interrupt output will also be set low on the first clock out negative transition. The interrupt source (alarm or clock out) can be determined by reading the interrupt status register. The clock output can be deselected by placing zero in the upper nibble of the con- trol register if the alarm function is selected as the only inter- rupt source. Counters The counter section consists of an on-board oscillator, a prescaler and 5 counters that hold the time of day/calendar information (see Figure 2). 1 of 4 possible external crystals determine the frequency of the on-board oscillator (32,768Hz, 1.048576MHz, 2.097152MHz, 4.194304MHz). The oscillator output is divided down by a pres- RESET AM - PM AND HOUR LOGIC PRESCALE OSCILLATOR SECOND XTAL XTAL MINUTE HOUR DAY MONTH FREEZE CIRCUIT CALENDAR LOGIC PRESCALE SELECT CLOCK SELECT CONTROL REGISTER INT. STATUS REGISTER CLOCK AND INT. LOGIC CLOCK OUT INT VDD VSS I/O INTERFACE SECOND LATCH MINUTE LATCH HOUR LATCH COMPARATOR DB0-DB7 A0 A1 A2 TPA IO/MEM TPB/WR RD CS POWER DOWN ADDRESS DECODE AND CONTROL LOGIC 8-BIT DATA BUS FIGURE 3. FUNCTIONAL DIAGRAM - ALARM CIRCUIT, CLOCK OUTPUT, INTERRUPT, AND STATUS REGISTERS HIGHLIGHTED CDP1879, CDP1879C-1 |
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Similar Description - CDP1879 |
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