AD7725 datasheet(22/28 Pages) AD

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REV. A

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AD7725

Status Register

The status register is a 16-bit register that provides the user with

information about the status of the device. The information avail-

able to the user includes whether a configuration file was loaded

successfully, what errors if any, occurred the last instruction

written, and other information that may be useful to the user

when operating the device. To read the status register, RS is

taken high and RD/

WR is taken high. When CS is taken low, the

contents of the status register will be output. The status register is

shown in Table II and the instruction set in Table III.

Table II. Status Register

Bit

Name

Function

InstrBUSY

This bit is set to 1 when an

instruction is performed.

Data Ready

This bit is set to 1 when data is

ready to be read from the device

(a read data cycle is required).

Data Request

This bit is set to 1 when the device.

requires data to be written to it (a write

data cycle is required).

ID Error

This bit is set to 1 if the programming

data has an incorrect ID value.

CRC Error

This bit is set to 1 if corrupt

data is loaded into the device.

Data Error

This bit is set to 1 if an overflow occurs

to indicate that the conversion result is

invalid.

InstrReg[15]

Instruction Register Bit 15

InstrReg[13]

Instruction Register Bit 13

InstrReg[12]

Instruction Register Bit 12

InstrReg[11]

Instruction Register Bit 11

InstrReg[6]

Instruction Register Bit 6

InstrReg[5]

Instruction Register Bit 5

InstrReg[4]

Instruction Register Bit 4

InstrReg[1]

Instruction Register Bit 1

InstrReg[0]

Instruction Register Bit 0

CFGEND

Configuration End Flag. This is set to 1

when the device has been configured

correctly and is ready to start converting.

Table III. Instruction Set for Parallel Mode

Instruction

Hex Code

Description

RdID

0x8802

Read Device ID

RdCONV

0x8D21

Read Converter Data. When

this instruction is issued to the

AD7725, the device continues to

output conversion data until the

ABORT instruction is issued.

WrConfig

0x1800

Write Configuration Data

WrConfigEM

0x1A00

Write Configuration Data,

Mask Errors

ABORT

0x0000

Abort. This instruction is a

soft reset, that is, it breaks the

conversion process and leaves

the device in a clean state,

still configured, ready for the

next instruction.

BFR

0x2000

Boot from Internal ROM

Configuring the Device

Following power-up, the AD7725 is configured by loading a user-

defined filter from an external source via the parallel interface.

Three instructions are provided for configuring the AD7725 (see

Table III).

•

WrConfig (Write Configuration)

When this instruction is issued, the device generates an

interrupt every time a new word of the configuration data is

required. The interrupt is cleared on the falling edge of

during the data write cycle. This continues until the com-

plete file is written. Immediately after the last word of the

configuration data is written, a final interrupt is asserted to

indicate “Instruction Done.”

However, if an error occurred during the configuration

process, for example, if the configuration data is corrupt or

in the wrong format, an interrupt will be asserted.

It is advised that when using this instruction, the status regis-

ter be read after each interrupt to ensure no errors occurred

and that the correct response is made. If configuration data is

corrupt, it will not be internally written to the postprocessor.

•

WrConfigEM (Write Configuration with Error Mask)

When this instruction is issued, no interrupts to signal errors

will ever be asserted during the download of the configura-

tion file. This saves reading the status register in response

to every interrupt as with the previous instruction. The

configuration process will always run through the 504

(42 writes

12 blocks) data write cycles in the configura-

tion file and once this is complete, the “Instruction Done”

interrupt is issued. In this case, the status register should be

checked at the end of the configuration to verify whether

any errors occurred. If configuration data is corrupt, it will

not be internally written to the postprocessor.

For evaluation purposes, the user can load the default filter

stored in internal ROM into the postprocessor. In this case the

following instruction should be issued:

•

BFR (Boot from ROM)

This instruction informs the device to load the configuration

data for the default filter stored in internal ROM.

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