DS1685/DS1687 3V/5V Real-Time Clocks FEATURES Incorporates Industry-Standard DS1287 PC Clock plus Enhanced Features Such as Y2K Compliant +3V or +5V Operation 64-Bit Silicon Serial Number Power-Control Circuitry Supports System Power-On from Date/Time Alarm or Key Closure 32kHz Output for Power Management Crystal-Select Bit Allows RTC to Operate with 6pF or 12.
DS1685/DS1687 3V/5V Real-Time Clocks ORDERING INFORMATION TEMP RANGE VOLTAGE (V) PIN-PACKAGE DS1685-3+ 0°C to +70°C 3 24 PDIP (0.600”) DS1685-3 DS1685-5+ 0°C to +70°C 5 24 PDIP (0.600”) DS1685-5 -40°C to +85°C 5 24 PDIP (0.600”) DS1685-5 DS1685E-3+ 0°C to +70°C 3 24 TSSOP (0.173”) DS1685E-3 DS1685E-5+ 0°C to +70°C 5 24 TSSOP (0.173”) DS1685E DS1685EN-3+ -40°C to +85°C 3 24 TSSOP (0.173”) DS1685E-3 DS1685EN-5+ -40°C to +85°C 5 24 TSSOP (0.
DS1685/DS1687 3V/5V Real-Time Clocks DETAILED DESCRIPTION The DS1685/DS1687 are real-time clocks (RTC) designed as successors to the industry-standard DS1285, DS1385, DS1485, and DS1585 PC RTCs. These devices provide the industry-standard DS1285 clock function with either +3.0V or +5.0V operation. The DS1685 also incorporates a number of enhanced features including a silicon serial number, power-on/off control circuitry, 242 bytes of user NV SRAM, and 32.
DS1685/DS1687 3V/5V Real-Time Clocks PIN DESCRIPTIONS PIN DS1685 DS1687 PDIP, SO, PLCC NAME FUNCTION PWR Active Low Power-On Output, Open Drain. The PWR pin is intended for use as an on/off control for the system power. With VCC voltage removed from the DS1685/DS1687, PWR can be automatically activated from a kickstart input by the KS pin or from a wake-up interrupt. Once the system is powered on, the state of PWR can be controlled by bits in the Maxim Integrated registers.
DS1685/DS1687 3V/5V Real-Time Clocks PIN DESCRIPTIONS (continued) PIN DS1685 DS1687 PDIP, SO, PLCC FUNCTION NAME EDIP TSSOP 18 19 20 21 22 22 23 24 25 26 18 19 — 21 22 KS Kickstart Input, Active Low. When VCC is removed from the DS1685/DS1687, the system can be powered on in response to an activelow transition on the KS pin, as might be generated from a key closure.
DS1685/DS1687 3V/5V Real-Time Clocks Figure 1.
DS1685/DS1687 3V/5V Real-Time Clocks Table 1. Crystal Specifications* PARAMETER SYMBOL 8B 9B Nominal Frequency Series Resistance Load Capacitance MIN fO ESR CL TYP 32.768 6, 12.5 MAX UNITS 50 kHz kΩ pF *The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications.
DS1685/DS1687 3V/5V Real-Time Clocks POWER-DOWN/POWER-UP CONSIDERATIONS The RTC function continues to operate, and all of the RAM, time, calendar, and alarm memory locations remain nonvolatile regardless of the level of the VCC input. . At least one back up supply must remain within the minimum and maximum limits whenever VCC is not at a valid level.
DS1685/DS1687 3V/5V Real-Time Clocks “don’t care” codes in all three time alarm bytes create an interrupt every second. The three time-alarm bytes can be used with the date alarm as described in the Wake-Up/Kickstart section. The century counter is discussed later in this text. All registers can be directly written or read except for the following: 1) Registers C and D are read-only. 2) Bit 7 of Register A is read-only. 3) Bit 7 of the seconds byte is read-only. Table 2A.
DS1685/DS1687 3V/5V Real-Time Clocks Table 2.
DS1685/DS1687 3V/5V Real-Time Clocks CONTROL REGISTERS The four control registers A, B, C, and D reside in both bank 0 and bank 1. These registers are accessible at all times, even during the update cycle. Register A (0Ah) MSB BIT 7 UIP BIT 6 DV2 BIT 5 DV1 BIT 4 DV0 BIT 3 RS3 BIT 2 RS2 BIT 1 RS1 LSB BIT 0 RS0 UIP – The update-in-progress (UIP) bit is a status flag that can be monitored. When the UIP bit is a 1, the update transfer occurs soon.
DS1685/DS1687 3V/5V Real-Time Clocks Register B (0Bh) MSB BIT 7 SET BIT 6 PIE BIT 5 AIE BIT 4 UIE BIT 3 SQWE BIT 2 DM BIT 1 24/12 LSB BIT 0 DSE SET – When the SET bit is a 0, the update transfer functions normally by advancing the counts once per second. When the SET bit is written to a 1, any update transfer is inhibited and the program can initialize the time and calendar bytes without an update occurring in the midst of initializing. Read cycles can be executed in a similar manner.
DS1685/DS1687 3V/5V Real-Time Clocks Register C (0Ch) MSB BIT 7 IQRF LSB BIT 0 0 10B BIT 6 PF BIT 5 AF BIT 4 UF BIT 3 0 BIT 2 0 BIT 1 0 IRQF – The interrupt-request flag (IRQF) bit is set to a 1 when one or more of the following are true: PF = PIE = 1 WF = WIE = 1 AF = AIE = 1 KF = KSE = 1 UF = UIE = 1 RF = RIE = 1 Any time the IRQF bit is a 1, the IRQ pin is driven low. Flag bits PF, AF, and UF are cleared after Register C is read by the program.
DS1685/DS1687 3V/5V Real-Time Clocks NV RAM—RTC The 242 general-purpose NV RAM bytes are not dedicated to any special function within the DS1685/DS1687. They can be used by the application program as nonvolatile memory and are fully available during the update cycle. The user RAM is divided into two separate memory banks. When the bank 0 is selected, the 14 RTC registers and 114 bytes of user RAM are accessible.
DS1685/DS1687 3V/5V Real-Time Clocks SQUARE-WAVE OUTPUT SELECTION The SQW pin can be programmed to output a variety of frequencies divided down from the 32.768kHz crystal tied to X1 and X2. The square-wave output is enabled and disabled by the SQWE bit in Register B or the E32K bit in extended register 4Bh. If the square wave is enabled (SQWE = 1 or E32K = 1), then the output frequency is determined by the settings of the E32K bit in Extended Register 4Bh and by the RS3–0 bits in Register A.
DS1685/DS1687 3V/5V Real-Time Clocks Table 3. Periodic Interrupt Rate and Square-Wave Output Frequency EXT. REG B SELECT BITS REGISTER A tPI PERIODIC INTERRUPT RATE SQW OUTPUT FREQUENCY E32K RS3 RS2 RS1 RS0 0 0 0 0 0 None None 0 0 0 0 1 3.90625ms 256Hz 0 0 0 1 0 7.8125ms 128Hz 0 0 0 1 1 122.070µs 8.192kHz 0 0 1 0 0 244.141µs 4.096kHz 0 0 1 0 1 488.281µs 2.048kHz 0 0 1 1 0 976.5625µs 1.024kHz 0 0 1 1 1 1.953125ms 512Hz 0 1 0 0 0 3.
DS1685/DS1687 3V/5V Real-Time Clocks Figure 4. Update-Ended And Periodic-Interrupt Relationship 1 second UIP tBUC UF tPI/2 tPI/2 PF t PI tPI = PERIODIC INTERRUPT TIME INTERNAL PER TABLE 3. tBUC = DELAY BEFORE UPDATE CYCLE = 244µs. EXTENDED FUNCTIONS The extended functions provided by the DS1685/DS1687 that are new to the RAMified RTC family are accessed by a software-controlled bank-switching scheme, as illustrated in Figure 5.
DS1685/DS1687 3V/5V Real-Time Clocks Figure 5.
DS1685/DS1687 3V/5V Real-Time Clocks SILICON SERIAL NUMBER A unique 64-bit lasered serial number is located in bank 1, registers 40h to 47h. This serial number is divided into three parts. The first byte in register 40h contains a model number, 71h, to identify the device type. Registers 41h to 46h contain a unique binary number. Register 47h contains a CRC byte used to validate the data in registers 40h to 46h. All 8 bytes of the serial number are read-only registers.
DS1685/DS1687 3V/5V Real-Time Clocks The timing associated with both the wake-up and kickstarting sequences is illustrated in the “Wake-Up/Kickstart Timing Diagram” in the Electrical Specifications section of this data sheet. The timing associated with these functions is divided into five intervals, labeled 1 to 5 on the diagram. The occurrence of either a kickstart or wake-up condition causes the PWR pin to be driven low, as described above.
DS1685/DS1687 3V/5V Real-Time Clocks 128 x 8 EXTENDED RAM The DS1685/DS1687 provides 128 x 8 of on-chip SRAM, which is controlled as nonvolatile storage sustained by VBAT and/or VBAUX. On power-up, the RAM is accessible after TREC. The on-chip 128 x 8 NV SRAM is accessed by the eight multiplexed address/data lines AD7–AD0. Access to the SRAM is controlled by two on-chip latch registers. One register is used to hold the SRAM address and the other register is used to hold read/write data.
DS1685/DS1687 3V/5V Real-Time Clocks Extended Control Register 4B MSB BIT 7 ABE BIT 6 E32K BIT 5 CS BIT 4 RCE BIT 3 PRS BIT 2 RIE BIT 1 WIE LSB BIT 0 KSE ABE – Auxiliary Battery Enable. This bit when written to a logic 1 enables the VBAUX pin for extended functions. E32K – Enable 32.768kHz output. This bit when written to a logic 1 enables the 32.768kHz oscillator frequency to be output on the SQW pin. This bit is set to a logic 1 when VCC is applied. CS – Crystal Select Bit.
DS1685/DS1687 3V/5V Real-Time Clocks The RTC address is latched on the falling edge of the ALE signal. Each time an RTC address is latched, the register address stack is pushed. The stack is only four registers deep, holding the three previous RTC addresses in addition to the current RTC address being accessed. The following waveform illustrates how the BIOS could recover the RTC address when an SMI occurs. ALE 1 2 3 4 1) The RTC address is latched.
DS1685/DS1687 3V/5V Real-Time Clocks ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground………………………………………………………………….0.3V to +6V Operating Temperature Range, Commercial ...……………………………………………………………….0°C to +70°C Operating Temperature Range, Industrial…………………………………………………………………...-40°C to +85°C Storage Temperature Range EDIP………………………………....……………………………………………………………………….-40°C to +85°C PDIP, SO, TSSOP……………………………….…………………………………....………………….-55°C to +125°C Lead Temperature (soldering, 10s)……….....
DS1685/DS1687 3V/5V Real-Time Clocks DC ELECTRICAL CHARACTERISTICS (VCC = 5.0V±10% or VCC = 3.0V±10%, TA = 0°C to +70°C, TA = -40°C to +85°C.) PARAMETER SYMBOL (-5) Average VCC PowerSupply Current MIN ICC1 TYP MAX 7 15 5 10 1 3 0.5 2 2B (-3) (-5) CMOS Standby Current (CS = VCC - 0.2V) ICC2 3B (-3) UNITS NOTES mA 2, 3 mA 2, 3 Input Leakage Current (Any Input) IIL -1 +1 µA Output Leakage Current IOL -1 +1 µA Output Logic 1 Voltage (IOUT = -1.0mA) VOH 2.
DS1685/DS1687 3V/5V Real-Time Clocks RTC AC TIMING CHARACTERISTICS (VCC = 3.
DS1685/DS1687 3V/5V Real-Time Clocks RTC AC TIMING CHARACTERISTICS (VCC = 5.0V±10%, TA = 0°C to +70°C, TA = -40°C to 85°C.
DS1685/DS1687 3V/5V Real-Time Clocks DS1685/DS1667 BUS TIMING FOR READ CYCLE TO RTC AND RTC REGISTERS DS1685/DS1687 BUS TIMING FOR WRITE CYCLE TO RTC AND RTC REGISTERS 28 of 34
DS1685/DS1687 3V/5V Real-Time Clocks POWER-UP/DOWN TIMING—5V (TA = +25°C) PARAMETER SYMBOL CS High to Power-Fail tPF Recovery at Power-Up tREC MIN TYP MAX UNITS 0 ns 150 NOTES ms VCC Slew Rate Power-Down tF 4.0 ≤ VCC ≤ 4.5V 300 µs VCC Slew Rate Power-Down tFB 3.0 ≤ VCC ≤ 4.0V 10 µs VCC Slew Rate Power-Up tR 4.5V ≥ VCC ≥ 4.
DS1685/DS1687 3V/5V Real-Time Clocks POWER-UP CONDITION—3V VIH CS tREC 2.7V 2.6V 2.5V VCC tR POWER FAIL POWER-DOWN CONDITION—3V CS VIH tPF tF VCC 2.7V 2.6V 2.
DS1685/DS1687 3V/5V Real-Time Clocks POWER-UP CONDITION—5V VIH CS tREC 4.5V 4.25V 4.0V VCC tR POWER FAIL POWER-DOWN CONDITION—5V CS VIH tPF tF VCC tFB 4.5V 4.25V 4.0V 3.
DS1685/DS1687 3V/5V Real-Time Clocks WAKE-UP/KICKSTART TIMING *THIS CONDITION CAN OCCUR WITH THE 3V DEVICE. NOTE: TIME INTERVALS SHOWN ABOVE ARE REFERENCED IN WAKE-UP/KICKSTART SECTION. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: All voltages are referenced to ground. Typical values are at +25°C and nominal supplies. Outputs are open. Applies to the AD0–AD7 pins and the SQW pin when each is in a high-impedance state. The IRQ and PWR pins are open-drain outputs.
DS1685/DS1687 3V/5V Real-Time Clocks PACKAGE INFORMATION For the latest package outline information and land patterns, go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
DS1685/DS1687 3V/5V Real-Time Clocks REVISION HISTORY REVISION DATE DESCRIPTION 4/10 Removed the leaded parts from the Ordering Information table; updated the storage temperature ranges, added the lead temperature, and updated the soldering temperature for all packages in the Absolute Maximum Ratings. 10/12 Correct Silicon Model number, correct hex address formatting.
