ADS8699IPWR datasheet(41/74 Pages) TI2

41 / 74 page

For a typical data transfer frame F:

1. The host controller pulls CONVST/CS low to initiate a data transfer frame. On the falling edge of the

CONVST/CS signal:

• RVS goes low, indicating the beginning of the data transfer frame.

• The internal SCLK counter is reset to 0.

• The device takes control of the data bus. As illustrated in Figure 7-25, the contents of the output data word

are loaded into the 32-bit output shift register (OSR).

• The internal configuration register is reset to 0000h, corresponding to a NOP command.

2. During the frame, the host controller provides clocks on the SCLK pin:

• On each SCLK capture edge, the SCLK counter is incremented and the data bit received on the SDI pin is

shifted into the LSB of the input shift register.

• On each launch edge of the output clock (SCLK in this case), the MSB of the output shift register data is

shifted out on the selected SDO-x pins.

• The status of the RVS pin depends on the output protocol selection (see the Protocols for Reading From

the Device section).

3. The host controller pulls the CONVST/CS pin high to end the data transfer frame. On the rising edge of

CONVST/CS:

• The SDO-x pins go to tri-state.

• As illustrated in Figure 7-25, the contents of the input shift register are transferred to the command

processor for decoding and further action.

• RVS output goes low, indicating the beginning of conversion.

After pulling CONVST/CS high, the host controller must monitor for a low-to-high transition on the RVS pin or

wait for the tconv_max time (see the Timing Requirements: Conversion Cycle table) to elapse before initiating a

new data transfer frame.

At the end of the data transfer frame F:

• If the SCLK counter = 32, then the device treats the frame F as an optimal data transfer frame for any read or

write operation. At the end of an optimal data transfer frame, the command processor treats the 32-bit

contents of the input shift register as a valid command word.

• If the SCLK counter is < 32, then the device treats the frame F as a short data transfer frame.

– The data write operation to the device in invalid and the device treats this frame as an NOP command.

– The output data bits transferred during a short frame on the SDO-x pins are still valid data. The host

controller can use the short data transfer frame to read only the required number of MSB bits from the 32-

bit output shift register.

• If the SCLK counter is > 32, then the device treats the frame F as a long data transfer frame. At the end of a

long data transfer frame, the command processor treats the 32-bit contents of the input shift register as a

valid command word. There is no restriction on the maximum number of clocks that can be provided within

any data transfer frame F. However, when the host controller provides a long data transfer frame, the last 32

bits shifted into the device prior to the CONVST/CS rising edge must constitute the desired command.

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ADS8691, ADS8695, ADS8699

SBAS777B – DECEMBER 2016 – REVISED MARCH 2021

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