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ICM7170AIPG Datasheet(PDF) 8 Page - Rochester Electronics |
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ICM7170AIPG Datasheet(HTML) 8 Page - Rochester Electronics |
8 / 14 page ICM7170 Specification Number ICM7170_IM (IL) REV - Page 8 of 14 7 Detailed Description Oscillator The ICM7170 has an onboard CMOS Pierce oscillator with an internally regulated voltage supply for maximum accuracy, stability, and low power consumption. It operates at any of four popular crystal frequencies: 32.768kHz, 1.046576MHz, 2.097152MHz, and 4.194304MHz (Note 1). The crystal should be designed for the parallel resonant mode of oscillation. In addition to the crystal, 2 or 3 load capacitors are required, depending on the circuit topology used. The oscillator output is divided down to 4000Hz by one of four divider ratios, determined by the two frequency selection bits in the Command Register (D0 and D1 at address 11H). This 4000Hz is then divided down to 100Hz, which is used as the clock for the counters. Time and calendar information is provided by 8 consecutive, programmable counters: 100ths of, seconds, minutes, hours, day of week, date, month, and year. The data is in binary format with 8 bits per digit. See Table 3 for address information. Any unused bits are held to a logic “0” during a read and ignored during a write operation. NOTE: 1. 4.94304MHz is not available over military temperature range. Alarm Compare RAM On the chip are 51 bits of Alarm Compare RAM grouped into words of different lengths. These are used to store the time, ranging from 10ths of seconds to years, for comparison to the real-time counters. Each counter has a corresponding RAM word. In the Alarm Mode an interrupt is generated when the current time is equal to the alarm time. The RAM contents are compared to the counters on a word by word basis. If a comparison to a particular counter is unnecessary, then the appropriate ‘M’ bit in Compare RAM should be set to logic “1”. The ‘M’ bit, referring to Mask bit, causes a particular RAM word to be masked off or ignored during a compare. Table 3 shows addresses and Mask bit information. Periodic Interrupts The interrupt output can be programmed for 6 periodic signals: 100Hz, 10Hz, once per second, once per minute, once per hour, or once per day. The 100Hz and 10Hz interrupts have instantaneous errors of ±2.5% and ±0.15% respectively. This is because non-integer divider circuitry is used to generate these signals from the crystal frequency, which is a power of 2. The time average of these errors over a 1 second period, however, is zero. Consequently, the 100Hz or 10Hz interrupts are not suitable as an aid in tuning the oscillator; the 1 second interrupt must be used instead. See General Notes, Note 6. The periodic interrupts can occur concurrently and in addition to alarm interrupts. The periodic interrupts are controlled by bits in the interrupt mask register, and are enabled by setting the appropriate bit to a “1” as shown in Table 4. Bits D1 through D6 in the mask register, in conjunction with bits D1 through D6 of the status register, control the generation of interrupts according to Figure 5. 0 1 1 1 1 0F RAM-day of week M - - - - 0 - 6 1 0 0 0 0 10 Interrupt Status and Mask Register + 1 0 0 0 1 11 Command register - - NOTES: Addresses 10010 to 11111 (12h to 1Fh) are unused. ‘+’ Unused bit for interrupt Mask Register, MSB bit for interrupt Status Register. ‘-’ Indicates unused bits. ‘ †’ AM/PM indicator bit in 12 hour format Logic “0” indicates AM, logic “1” indicates PM. ‘M’ Alarm compare for particular counter will be enabled if bit is set to logic “0”. TABLE 3. ADDRESS CODES AND FUNCTIONS (Continued) ADDRESS FUNCTION DATA VALUE A4 A3 A2 A1 A0 HEX D7 D6 D5 D4 D3 D2 D1 D0 TABLE 4. INTERRUPT AND STATUS REGISTERS FORMAT INTERRUPT MASK REGISTER ADDRESS (10000b, 10h) WRITE-ONLY D7 D6 D5 D4 D3 D2 D1 D0 NOT USED DAY HOUR MIN SEC 1/10 SEC 1/100 SEC ALARM ← Periodic Interrupt Mask Bits → Alarm/Compare Mask Bit INTERRUPT STATUS REGISTER ADDRESS (10000b, 10h) READ-ONLY D7 D6 D5 D4 D3 D2 D1 D0 GLOBAL INTERRUPT DAY HOUR MIN SEC 1/10 SEC 1/100 SEC ALARM Periodic and Alarm Flags ← Periodic Interrupt Flags → Alarm Compare Flag ICM7170 |
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