AS8500 - Data Sheet

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Revision 1.2, 08-Junel-06

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The slave unit drives the sdat signal only in master-read data condition. In all other cases the slave sdat pin is in high-impedance state. During

data transfer in read condition the internal AD-conversion in continuing but the data in the MSR-register is not updated and the output of the

INTN signal is suppressed. Only after the completion of the reading cycle the ASSP returns to the normal condition and updates the MSR-

register immediately if a new AD-conversion has been finished during data transfer.

The master unit does not detect any bus conditions since it generates them. Data transfer conditions (direction, register address and register

data) must not be changed until the current condition is over. The slave unit does not detect start and exception condition when master-read is

in progress.

The exception condition is reserved for future use and should be avoided.

8.4

Data transfers

Generally the SDI interface is active in all ASSP modes. For security reasons some write operations are restricted to certain modes. Read

operations are never disabled in order to keep consistent sdat driving conditions.

Writing to the result, trimming and calibration registers (MSR, CAR and TRR) is allowed only in test modes.

Writing to the Zener-Zap register is allowed only in mode MZP.

The first data bit after the start condition in each data transfer defines the data direction: sdat=high is used for master-read data (mr) condition

and sdat=low for master-write data (mw) condition.

Data is transferred with the most significant bit (MSB) first. Data bits are composed of register address and register data bits. Register address

is transmitted first, followed by the register data bits. The register address is always 4 bits long. The number of register data bits (see 7.5) is

implied by the register address.

Figure 7: SDI Data transfer

The ASSP supports the data transfers presented in the following table:

master read-write operations

REGISTER

ADDRESS

Contents

read

allowed in

modes

write allowed in

modes

page

OPM

0

operating mode

All

All

CRA

1

measurement set-up A

All

All

CRB

2

measurement set-up B

All

All

CRG

3

general measurement conditions

All

All

MSR

4

measurement result

All

>7

ZZR

5

Zener-Zap data

All

5

CAR

6

calibration register

All

>7

LSB

MSB

a0

a1

a2

a3

Register data

sclk

sdat

Register address

Direction

mw

mr