AD7280 datasheet(29/33 Pages) AD

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Preliminary Technical Data

AD7280

Rev. PrD | Page 29 of 33

READING DATA FROM THE AD7280

There are a number of read options available on the AD7280.

The user may read back the results from all the conversions

completed on an individual part in the chain, from all the

conversions completed on all parts in the chain or from

individual registers on selected parts in the chain.

In each case the user is required to first write to the Read

correct data on the outputs. When reading back an individual

the read register of the selected part. When reading back

conversion results from any or all parts in the chain an address

of 0h should be written to the read register of the selected parts.

When the address written to the read register is 0h the

conversion results selected for read back are controlled by

setting bits D13 and D12 of the Control register. Please refer to

Table 14. This allows the user to select 4 different read back

options

•

Read back 12 conversion results: 6 voltage and 6

temperature

•

Read back 9 conversion results: 6 voltage and 3

temperature

•

Read back 6 conversion results: 6 voltage results only

•

Switch off read operation on this part

If the user wishes to read back the conversion results from a

single AD7280 in the daisy chain bits D13 and D12 of the

control register on that part should be set to select the correct

conversion results. Bits D13 and D12 on all other AD7280s in

the daisy chain should be set to switch off the read operation on

those parts. It should be noted that it is more efficient in terms

of 24-bit write cycles to first switch off the read operation on all

AD7280s in the daisy chain. This can be achieved with a single

write cycle, using bit D3 to address all parts in the chain. The

user may then address the individual part and set bits D13 and

D12 to select the required conversion results.

When reading back conversion data from any, or all, of the

AD7280s in a daisy chain the conversion results returned from

the AD7280 will be the last completed conversion on that part.

It is recommended that the user also set bits D15 and D14 of

the control register, to select the number of conversions to be

completed on each part, and initiate the conversions through

either the CNVST pin or the rising edge of CS., as part of the

read operation. This allows the user to implement a simple

convert and read back routine with the most efficient number

of 24-bit write and read operations. A general example of this

routine, which would convert and read back from all parts in

the AD7280 daisy chain would be:

•

Write0h to the Read register on all of the parts in the

daisychain. Note: 0h is the default value of this register

on power up and following a reset operation.

•

Write to the Control register on all parts. Set bits D15

and D14 to select the required conversions. Set bits

D13 and D12 to select the required conversion results

for read back.

•

Initiate the conversions through either the falling edge

of CNVST or the rising edge of CS.

•

Allow sufficient time for each conversion to be

completed. Please refer to Converting Cell Voltages

and Temperatures section.

•

Either bring CS low and apply 24 SCLKs for each

conversion result to be read back or apply an

individual CS pulse, each framing 24 SCLKs, for

each conversion result to be read back.

The following section outlines ten examples of Conversion and

/or Readback routines which would be commonly used in an

application using a chain of AD7280s to monitor the voltage

and/or temperature of the a stack of Lithium Ion batteries.

Convert and Read all parts, all voltages and all

temperatures

•

Bits D15-D12 of the CONTROL register should be set

to 0 on all parts.

•

Initiate conversion through either the falling edge of

CNVST or the rising edge of CS.

•

Following the completion of the conversion bring CS

low and apply 24 SCLKs for each voltage and

temperature result to be read back.

Convert and Read all parts, all voltages and three

temperatures per part

•

Bits D15 and D13 of the CONTROL register should

be set to 0, bits D14 and D12 should be set to 1 on all

parts.

•

Initiate conversion through either the falling edge of

CNVST or the rising edge of CS.

•

Following the completion of the conversion either

bring CS low and apply 24 SCLKs for each conversion

result to be read back or apply an individual CS

pulse, each framing 24 SCLKs, for each conversion

result to be read back.

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