DS2755E 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS2755E

High-Accuracy Battery Fuel Gauge with Snapshot

Dallas Semiconductor -> Maxim Integrated 

DS2755: High-Accuracy Battery Fuel Gauge with Snapshot

Figure 8. TEMPERATURE REGISTER FORMAT

MSB—Address 18

S 29 28 27 26 25 24 23

MSb

LSb

LSB—Address 19

22 21 20 X X X X X

MSb

LSb

Units: 0.125°C

PROGRAMMABLE I/O

The PIO pin can be used as a general purpose programmable I/O pin, or as an interrupt output to alert the system

of a critical change in Temperature or ACR registers. To use the PIO pin in the programmable I/O mode described

in this section, the PIO interrupt method must not be enabled. See the Interrupt Signaling section.

As a programmable I/O pin, PIO provides a digital input or an open drain digital output. Writing a 1 to the PIO bit in

the Special Feature Register disables the output driver. With the PIO pin Hi-Z, it can be used as an input. The logic

level of the PIO pin is reported when the Special Feature Register is read via the serial interface.

To use the PIO pin as an output, write the desired output value to the PIO bit in the Special Feature Register.

Writing a 0 to the PIO bit enables the PIO output driver, pulling the PIO pin to VSS. As stated above, writing a 1 to

the PIO bit forces the pin to a Hi-Z state. A pullup resistor or current source must be provided to force the pin high.

The PIO pin can be biased several volts above VDD allowing inter-operation with a system voltage which is higher

than the battery voltage. Consult the Absolute Maximum Ratings table when operating the PIO pin significantly

above VDD. The DS2755 turns off the PIO output driver and sets the PIO bit high when in Sleep mode or when DQ

is low for more than tSLEEP, regardless of the state of the PMOD bit.

INTERRUPT SIGNALING

The interrupt feature is enabled by setting the Interrupt Enable (IE) bit (bit 2 in the Special Feature Register). When

IE is set, an interrupt will be signaled if the alarm comparator thresholds are crossed. A 1-Wire RESET clears IE.

The host must re-enable interrupts by setting IE in the last transaction on the bus.

The interrupt signal pin is selected by setting or clearing the Interrupt Output Select (IOS) bit (bit 2 in the Status

Register). When IOS is set, the DQ pin performs the interrupt signaling, when IOS is cleared, the PIO pin performs

the interrupt signaling.

DQ signals an interrupt condition by driving the 1-Wire bus low for tIL μs. The DS2755 and all other 1-Wire devices

present on the bus interpret this signal as a 1-Wire RESET. A Presence Pulse should be expected from all 1-Wire

devices, including the DS2755 following the interrupt signal. The host system can sense the interrupt signal on the

falling or rising edge of either the RESET or Presence Pulse.

PIO signals an interrupt by driving low. PIO remains low until the host clears the condition by writing a 1 to the PIO

bit (bit 7 in the Special Feature Register). A pullup resistor or current source must be provided to force the pin high.

The host can sense the interrupt on the falling edge of PIO.

ALARM COMPARATORS

Interrupt threshold values can be programmed by the user in the designated SRAM memory registers in the

formats and locations found in Figure 9. Since these thresholds are located in SRAM memory, they must be

reprogrammed if a loss of power to the DS2755 occurs. The DS2755 interrupts the system host to indicate that one

of the following events has occurred:

ƒ Accumulated Current ≥ Current Accumulator Interrupt High Threshold

ƒ Accumulated Current ≤ Current Accumulator Interrupt Low Threshold

ƒ Temperature ≥ Temperature Interrupt High Threshold

ƒ Temperature ≤ Temperature Interrupt Low Threshold

The host may then poll the DS2755 to determine which threshold has been met or exceeded.

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