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AD7790 Datasheet(PDF) 11 Page - Analog Devices
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AD7790 Datasheet(HTML) 11 Page - Analog Devices
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Rev. A | Page 11 of 20
STATUS REGISTER (RS1, RS0 = 0, 0; POWER-ON/RESET = 0x88)
The status register is an 8-bit read-only register. To access the ADC status register, the user must write to the communications register,
select the next operation to be a read, and load bits RS1 and RS0 with 0. Table 8 outlines the bit designations for the status register. SR0
through SR7 indicate the bit locations, SR denoting the bits are in the status register. SR7 denotes the first bit of the data stream. The
number in brackets indicates the power-on/reset default status of that bit.
Table 8. Status Register Bit Designations
Ready bit for ADC. Cleared when data is written to the ADC data register. The RDY bit is set automatically
after the ADC data register has been read or a period of time before the data register is updated with a
new conversion result to indicate to the user not to read the conversion data. It is also set when the part
is placed in powe-down mode. The end of a conversion is indicated by the DOUT/RDY pin also. This pin
can be used as an alternative to the status register for monitoring the ADC for conversion data.
ADC Error Bit. This bit is written to at the same time as the RDY bit. Set to indicate that the result written
to the ADC data register has been clamped to all 0s or all 1s. Error sources include overrange, under-
range. Cleared by a write operation to start a conversion.
This bit is automatically cleared.
This bit is automatically cleared.
This bit is automatically set.
This bit is automatically cleared if the device is an AD7790. It can be used to distinguish between the
AD7790 and AD7791, in which the bit is set.
These bits indicate which channel is being converted by the ADC.
MODE REGISTER (RS1, RS0 = 0, 1; POWER-ON/RESET = 0x02)
The mode register is an 8-bit register from which data can be read or to which data can be written. This register is used to configure the
ADC for range, enable or disable the buffer, or place the device into power-down mode. Table 9 outlines the bit designations for the mode
register. MR0 through MR7 indicate the bit locations, MR denoting the bits are in the mode register. MR7 denotes the first bit of the data
stream. The number in brackets indicates the power-on/reset default status of that bit. Any write to the setup register resets the modulator
and filter and sets the RDY bit.
Table 9. Mode Register Bit Designations
Mode Select Bits. These bits select between continuous conversion mode, single conversion mode, and
standby mode. In continuous conversion mode, the ADC continuously performs conversions and places
the result in the data register. RDY goes low when a conversion is complete. The user can read these
conversions by placing the device in continuous read mode whereby the conversions are automatically
placed on the DOUT line when SCLK pulses are applied. Alternatively, the user can instruct the ADC to
output the conversion by writing to the communications register. After power-on, the first conversion is
available after a period 2/ f
while subsequent conversions are available at a frequency of f
. In single
conversion mode, the ADC is placed in power-down mode when conversions are not being performed.
When single conversion mode is selected, the ADC powers up and performs a single conversion, which
occurs after a period 2/f
. The conversion result in placed in the data register, RDY goes low, and the
ADC returns to power-down mode. The conversion remains in the data register and RDY remains active
(low) until the data is read or another conversion is performed. See Table 10.
Range Bits. The AD7790 can be operated with four analog input ranges (see Table 11).
Burnout Current Enable Bit. When this bit is set to 1 by the user, the 100 nA current sources in the signal
path are enabled. When BO = 0, the burnout currents are disabled. The burnout currents can be enabled
only when the buffer is active.
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