AS3911 datasheet(59/149 Pages) AMSCO

59 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 59

Appl icatio n I n f o rm a t i o n

Measure Capacitance

This command performs the capacitance measurement. See

“Capacitive Sensor” on page 14 for more details.

Duration time: 250 μs max.

In order to avoid interference with Xtal oscillator and reader

magnetic field it strongly recommended to use this command

in Power-down mode only.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after

command execution is terminated.

Measure Power Supply

This command performs the power supply measurement.

Configuration bits mpsv1 and mpsv0 of the Regulator Voltage

Control Register define which power supply is measured (VDD,

VSP_A, VSP_D and VSP_RF can be measured). Result of

measurement is stored in the A/D Converter Output Register.

During the measurement the selected supply input is

connected to a 1/3 resistive divider output of which is

multiplexed to A/D converter in absolute mode. Due to 1/3

division one LSB represents 23.438 mV.

Duration time: 25 μs max.

This command is accepted in case en (bit 7 of the Operation

Control Register) is set and Xtal oscillator frequency is stable.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after

command execution is terminated.

Start Timers

See “Timers” on page 29.

Registers

The 6-bit register addresses below are defined in the

hexadecimal notation. The possible address range is from 00h

to 3Fh.

There are two types of registers implemented in the AS3911:

configuration registers and display registers. The configuration

registers are used to configure the AS3911. They can be written

and read through the SPI (RW). The display registers are read

only (RO); they contain information about the AS3911 internal

state.

Registries are set to their default state at power-up and after

sending direct command Set Default. The only exceptions are

the IO Configuration Register 1 and the IO Configuration

Configuration bits of these two registries are related to

hardware configuration which is in most cases not going to

change during the operation.

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