AD7992 datasheet(19/29 Pages) AD

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AD7992

Rev. 0 | Page 18 of 28

CONVERSION RESULT REGISTER

The conversion result register is a 16-bit, read-only register that

stores the conversion result from the ADC in straight binary

format. A 2-byte read is needed to read data from this register.

Table 12 shows the contents of the first byte to be read from the

AD7992, and Table 13 shows the contents of the second byte.

Table 12. Conversion Value Register (First Read)

D15

D14

D13

D12

D11

D10

Alert_Flag

Zero

CHID0

MSB

B10

Table 13. Conversion Value Register (Second Read)

The AD7992 conversion result consists of an Alert_Flag bit, two

leading zeros, a channel identifier bit, and the 12-bit data result.

The Alert_Flag bit indicates whether the conversion result

being read or any other channel result has violated the limit

registers associated with it. If an ALERT occurs, the master may

wish to read the ALERT status register to obtain more informa-

tion on where the ALERT occurred if the Alert_Flag bit is set.

The Alert_Flag bit is followed by two leading zeros and a

channel identifier bit that indicate to which channel the con-

version result corresponds. When this bit is 0, the conversion

result corresponds to VIN1, and when it is 1, the conversion

result corresponds to VIN2. These, in turn, are followed by the

12-bit conversion result, MSB first.

LIMIT REGISTERS

The AD7992 has two pairs of limit registers. Each pair stores

high and low conversion limits for both analog input channels.

Each pair of limit registers has one associated hysteresis register.

All 6 registers are 16 bits wide; only the 12 LSBs of the registers

are used. On power-up, the contents of the DATAHIGH register

for each channel are full scale, while the contents of the

DATALOW registers are zero scale by default.

The limit registers can be used to monitor the conversion

results on one or both channels. The AD7992 signals an

ALERT (in either hardware or software or both, depending

on the configuration) if the result moves outside the upper or

lower limit set by the user.

DATAHIGH Register CH1/CH2

The DATAHIGH register for a channel is a 16-bit, read/write

stores the upper limit that activates the ALERT output and/or

the Alert_Flag bit in the conversion result register. If the value

in the conversion result register is greater than the value in the

DATAHIGH register, an ALERT occurs. When the conversion

result returns to a value at least N LSB below the DATAHIGH

reset. The value of N is taken from the 12-bit hysteresis register

associated with that channel. The ALERT pin can also be reset

by writing to Bits D2 and D1 in the configuration register.

Table 14. AD7992 DATAHIGH Register (First Read/Write)

D15

D14

D13

D12

D11

D10

B11

B10

Table 15. AD7992 DATAHIGH Register (Second Read/Write)

DATALOW Register CH1/CH2

The DATALOW register for each channel is a 16-bit read/write

stores the lower limit that activates the ALERT output and/or

the Alert_Flag bit in the conversion result register. If the value

in the conversion result register is less than the value in the

DATALOW register, an ALERT occurs. When the conversion

result returns to a value at least N LSB above the DATALOW

reset. The value of N is taken from the hysteresis register

associated with that channel. The ALERT output pin can also be

reset by writing to Bits D2 and D1 in the configuration register.

Table 16. DATALOW Register (First Read/Write)

D15

D14

D13

D12

D11

D10

B11

B10

Table 17. DATALOW Register (Second Read/Write)

Hysteresis Register (CH1/CH2)

Each hysteresis register is a 16-bit read/write register; only

the 12 LSBs of the register are used. The hysteresis register

stores the hysteresis value, N, when using the limit registers.

Each pair of limit registers has a dedicated hysteresis register.

The hysteresis value determines the reset point for the ALERT

pin/Alert_Flag if a violation of the limits has occurred. For

example, if a hysteresis value of 8 LSB is required on the

upper and lower limits of Channel 1, the 16 bit word,

0000 0000 0000 1000, should be written to the hysteresis

On power-up, the hysteresis registers contain a value of 8 LSB.

If a different hysteresis value is required, that value must be

written to the hysteresis register for the channel in question.

Table 18. Hysteresis Register (First Read/Write)

D15

D14

D13

D12

D11

D10

B11

B10

Table 19. Hysteresis Register (Second Read/Write)

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