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Preliminary Technical Data

AD7294

HYSTERESIS REGISTERS

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

12 LSBs of the register are used, with the MSB signaling the

alert event. 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 occurs. 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

registers contain a value of 8 LSB for non-temperature result

registers and 8 °C, or 32 LSB, for the TSENSE registers. If a

different hysteresis value is required, that value must be written

to the hysteresis register for the channel in question. For the

TSENSE register D11, in Table 23 is 0.

Table 23. Hysteresis Register (First Read/Write)

MSB

LSB

D15

D14

D13

D12

D11

D10

Alert_Flag

B11

B10

Table 24. Hysteresis Register (Second Read/Write)

MSB

LSB

Using the Limit Registers to

Store Min/Max Conversion Results

If full scale—that is, all 1s—is written to the hysteresis register

for a particular channel, the DATAHIGH and DATALOW registers

for that channel no longer act as limit registers as previously

described, but act as storage registers for the maximum and

minimum conversion results returned from conversions on a

channel over any given period of time. This function is useful in

applications where the widest span of actual conversion results

is required rather than using the ALERT to signal that an

intervention is necessary. Note that on power-up, the contents

of the DATAHIGH register for each channel are full scale, whereas

the contents of the DATALOW registers are zero scale by default.

Therefore, minimum and maximum conversion values being

stored in this way are lost if power is removed or cycled.

Rev. PrB | Page 29 of 45

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