ADBMS2950BCCSZ datasheet(24/97 Pages) AD

24 / 97 page

ADBMS2950B

Data Sheet

Rev. 0 | Page 24 of 97

Table 31. Write Data PEC Format

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

DPEC0

PEC[9]

PEC[8]

DPEC1

PEC[7]

PEC[6]

PEC[5]

PEC[4]

PEC[3]

PEC[2]

PEC[1]

PEC[0]

Table 32. Read Command Counter and Data PEC Format

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

DPEC0

CCNT[5]

CCNT[4]

CCNT[3]

CCNT[2]

CCNT[1]

CCNT[0]

PEC[9]

PEC[8]

DPEC1

PEC[7]

PEC[6]

PEC[5]

PEC[4]

PEC[3]

PEC[2]

PEC[1]

PEC[0]

Command Counter

A command counter, CCNT[5:0] as shown in Table 32,

enhances system level software diagnostics and communication

integrity. The command counter is initialized to 0 on power

cycling, by the SRST or by the RSTCC command. The

command counter increments if ADBMS2950B receives a

command without data, which are the 4-byte commands like

SNAP, UNSNAP, and ADI1, or if it receives a command with

write data such as WRCFGA and CLRFLAG. For a command to

be received, the command PEC and data PEC should match.

When the command counter increments past the maximum

value of 63, it rolls over to a value of 1, not 0. The 0 value is

reserved for specific reset cases listed previously. All read

commands return the register data followed by the command

counter and data PEC.

The host controller can keep track of the expected command

counter while sending commands and compare it with the

CCNT value received from the ADBMS2950B with every read

command. It is the responsibility of the host controller to

confirm that SPI frames are received in time as expected, to

verify the data checksum, and to track the command counter.

Polling Methods

Single Device SPI Polling

In configurations that communicate in SPI mode, there are two

methods of polling. The first method is to hold CSB low after an

ADC conversion command is sent. After entering a conversion

command, the SDO line is driven low when the device is busy

performing conversions. SDO is pulled high when the device

completes conversions. However, the SDO also returns to high

when CSB goes high even if the device has not completed the

conversion (see Figure 23). A problem with this method is that

the controller is not free to do other serial communication

while waiting for ADC conversions to complete.

The next method overcomes this limitation. The controller can

send an ADC command, perform other tasks, and then send a

Poll command to determine the status of the ADC conversions.

After entering the Poll command, SDO goes low if the device is

busy performing operations. SDO is pulled high at the end of

operations. However, SDO also goes high when CSB goes high,

even if the device has not completed the operation.

Figure 23. SDO Polling After an ADC Conversion Command (Single Device Configuration)

Figure 24. SDO Polling Using PLADC Command (Single Device Configuration)

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