In manual mode, the channel ID of the desired analog input is configured in the CHANNEL_ID register. On power-up or after device reset, AIN0 is selected and CHANNEL_ID[2:0] = 000b. Manual mode can be enabled from any other sequencing mode by programming the SEQ_MODE[1:0] bits to 00b in the DEVICE_CFG register. Figure 42 shows the timing information for changing channels in manual mode.
The channel information can be updated in a microcontroller (MCU)-friendly 3-byte access. As the 24-bits of channel configuration are sent over SDI, conversion data are clocked out over SDO. The data on SDO are MSB aligned and the first 16 clocks correspond to 16 bits of conversion data. The last eight bits of the SDO can be ignored by the MCU.
As shown in Figure 42, the command to switch to AINy is sent in the Nth cycle and the data corresponding to channel AINy is available in the (N + 2)th cycle. This switch occurs because the SDI commands are processed and the ADC starts conversions on the rising edge of CS. Thus, the conversion is processed on the previous channel (AINx) and not on the updated channel ID (AINy).
As shown in Figure 43, after selecting AINy the output of the multiplexer does not create a charge kickback as long as SDI is set to 0 (that is, as long as SDI returns the NOP command). Therefore, high-impedance sources such as the voltage from resistor dividers can be connected to the analog inputs of the multiplexer without an op amp.