DS1238 Dallas, DS1238 Datasheet
DS1238
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DS1238 Summary of contents
Page 1
... When an out-of-tolerance condition occurs, the microprocessor reset and power-fail outputs are forced active, and static RAM control unconditionally write protects external memory. The DS1238 also provides early warning detection of a user-defined threshold by driving a non-maskable interrupt. External reset control is provided by a pushbutton reset ...
Page 2
... RST so that the , RST and RVT RST The V for the 5% operation option (DS1238-5) is set for 4.75 volts (4.62 typical). The RST and CCTP signals are excellent for microprocessor reset control, as processing is stopped at the last possible moment of in-tolerance power up, CC the RST and ...
Page 3
... DS1238 FUNCTIONAL BLOCK DIAGRAM Figure 1 WATCHDOG TIMER The DS1238 provides a watchdog timer function which forces the active state when the strobe input ( is described below in Table 1. The watchdog timeout period begins as soon as RST and If a high-to-low transition occurs at the to time out again. The input timing is shown in Figure 2 ...
Page 4
... RST or NMI When the supply being monitored decays to the voltage sense point, the DS1238 will force the output to an active state. Noise is removed from the time domain hysteresis. That is, the monitored supply is sampled periodically at a rate determined by an internal ring oscillator running at approximately 30kHz (33 s/cycle) ...
Page 5
... PUSHBUTTON RESET TIMING Figure 4 Watchdog Timeout Period (typ) First Period Other Timeout Following a Reset 20480 Clks 5120 Clocks 2.2 sec 550 ms X Cpf 2.7 sec 170 ms 2.7 sec 2.7 sec is below DS1238 Reset Active Duration 641 Clks Cpf X Cpf BAT ...
Page 6
... NON-MASKABLE INTERRUPT Figure 1.27 SENSE R2 V SENSE MAXVOLTAGE = 1.27 Example 1: 5 Volt Supply 10k Ohms 4.8 Volts SENSE R1 10k 4 1. 27.8k Ohm 10k FROM IN INPUT Figure 6 NMI x 5.0 = VMAX Example 2: 12 Volt Supply 10k Ohms 9.0 Volts SENSE R1 9 MAX 10k x 1. 60.9k Ohm 10k 9.00 x 5.0 = 35.4 Volts 1.27 DS1238 ...
Page 7
... MEMORY BACKUP The DS1238 provides all of the necessary functions required to battery back a static RAM. First, an internal switch is provided to supply SRAM power from the primary 5-volt supply (V external battery (V ), whichever is greater. Second, the same power-fail detection described in the BAT power monitor section is used to hold the chip enable output ( ...
Page 8
... NONVOLATILE SRAM Figure 7 FRESHNESS SEAL Figure 8 Note: This series of pulses must be applied during normal +5 volt operation DS1238 ...
Page 9
... POWER SWITCHING Figure 9 Note: If freshness on the DS1238 is not used, and V for system use. BAT01 TIMING DIAGRAMS This section provides a description of the timing diagrams shown in Figure 10 and Figure 11. Figure 10 illustrates the relationship for power down the processor is notified of an impending power failure via an active to save critical data in nonvolatile SRAM ...
Page 10
... POWER-DOWN TIMING Figure DS1238 ...
Page 11
... POWER-UP TIMING Figure DS1238 ...
Page 12
... MAX UNITS NOTES 5.0 5.5 V 5 MAX UNITS NOTES 4 mA 200 nA 100 -0.8 V 0.4 V -0.1V V -0.8 V +1.0 A +1 4.37 4.50 V 4.62 4.75 V +1.0 A 1.27 1.35 V DS1238 10 121 ...
Page 13
... RPU t 10 FB1 t 0.1 REC 1.7 2.7 TD 110 170 t 20480 TD 5120 t PPF f 0 OSC SYMBOL MIN TYP OUT DS1238 = 5V 10%) CC MAX UNITS NOTES 175 s 175 s 150 100 ns 150 ...
Page 14
... DS1238 can supply at V CCO1 during normal 5-volt operation the maximum average load which the DS1238 can supply through the V CCO2 retention battery supply operation, with a maximum drop of 0.8 volts for commercial, 1.0V for industrial. 5. With ...