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S4261PAS Arkusz danych(PDF) 13 Page - Summit Microelectronics, Inc. |
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S4261PAS Arkusz danych(HTML) 13 Page - Summit Microelectronics, Inc. |
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13 / 16 page ![]() S4242/S42WD42/S4261/S42WD61 13 2025 6.0 4/17/00 Watchdog Timer Operation The S42WD42/S42WD61 has a watchdog timer with a nominal timeout period of 1.6 seconds. Whenever the watchdog times out it will generate a reset output on both RESET# and RESET. The watchdog timer will reset to t0 whenever the S42WD42/S42WD61 issues an ACKnowl- edge. Therefore, the host system will need to issue a start condition, followed by a valid address and command. It can be a normal command as in the sequence of reading or writing to the memory, or it can be a dummy command issued solely for the purpose of resetting the watchdog timer. Refer to Figure 17 for detailed sequence of opera- tions. The watchdog timer will be held in the reset state during power-on while VCC is less than VTRIP. Once VCC exceeds FIGURE 17. SEQUENCE ONE FIGURE 18. SEQUENCE TWO VTRIP, the watchdog will continue to be held in a reset state for the duration of tPURST. After tPURST, the timer will be released and begin counting. If either reset input is asserted the watchdog timer will be reset and remain in the reset condition until either tPURST has expired or the reset input is released, whichever is longer. If the watchdog times out and no action is taken by the host, the S42xxx will drive the reset outputs active for the duration of tPURST at which point it will release the outputs and begin the watchdog timer again. Refer to Figure 18 for detailed sequence of operations. S T A R T 1 0x 1 0 x x A C K S T O P R W S T A R T 1 0x 1 0 x x A C K S T O P R W SCL and SDA Idle ACK response from S42xxx Resets The Watchdog Timer t < 1.6sec S T A R T 1 0x 1 0 x x S T O P R W SCL and SDA Idle t > 1.6sec A C K t0 t0 t0 tPURST 2025 T fig17 2.0 RESET# 2025 T fig18 2.0 RESET# S T A R T 1 0x 1 0 x x A C K S T O P R W A C K SCL and SDA Idle S T A R T 1 0x 1 0 x x S T O P R W SCL and SDA Idle t > 1.6sec Watchdog Timer t0 t0 t > 1.6sec tPURST t0 No Affect On tPURST |
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