DS1994 Просмотр технического описания (PDF) - Maxim Integrated

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DS1994

4Kb Plus Time Memory iButton®

Maxim Integrated 

DS1994

Spontaneous interrupts are signaled by the DS1994 by pulling the data line low for 960s to 3840s as

the interrupt condition begins (Figure 12). After this long low pulse, a presence pulse follows. If the alarm

condition occurs just after the master has sent a reset pulse, i.e., during the high or low time of the

presence pulse, the DS1994 does not assert its interrupt pulse until the presence pulse is finished (Figure

13).

If the DS1994 cannot assert a spontaneous interrupt, either because the data line was not pulled high,

communication was in progress, or the interrupt was not armed, it extends the next reset pulse to a total

length of 960s to 3840s (delayed interrupt). If the alarm condition occurs during the reset low time of

the reset pulse, the DS1994 immediately asserts its interrupt pulse; thus, the total low time of the pulse

can be extended up to 4800s (Figure 14). If a DS1994 with a not previously signaled alarm detects a

power-on cycle on the 1-Wire bus, it sends a presence pulse and waits for the reset pulse sent by the

master to extend it and to subsequently issue a presence pulse (Figure 15). As long as an interrupt has not

been acknowledged by the master, the DS1994 continues sending interrupt pulses.

The interrupt signaling discussed so far is valid for the first opportunity the device has to signal an

interrupt. It is not required for the master to acknowledge an interrupt immediately. If an interrupt is not

acknowledged, the DS1994 continues signaling the interrupt with every reset pulse. To do so, the DS1994

either uses the waveform of the type 2 interrupt (Figure 14) or the waveform of the type 1A interrupt

(Figure 13). The waveform of the type 2 interrupt is observed after a communication to a device other

than the interrupting one; after successful communication to the interrupting device (without

acknowledging the interrupt), the waveform of the type 1A interrupt is found.

Figure 12. TYPE 1 INTERRUPT

VPUP

RESET

PULSE

1-WIRE

BUS

GND

PRESENCE

PULSE

INTERRUPT PULSE

960µs - 3840µs

PRESENCE

PULSE

Note: No communication following

presence pulse, i. e., no falling edge.

Interrupt condition occurs here.

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