USB-I/O Interface Adapter GPIO-24. Programmer's Reference Manual.

Command is an 8-byte array of the following format:

Byte 0: GPIO_SET_ADC_MODULE_CFG (0x20)

This byte contains command ID (command type). It must be set to 0x20.

Byte 1: ECHO

This byte is used to associate a response received from GPIO-24 adapter with a specific command. Response will contain exactly the same value in its echo byte.

Byte 2: ON

The ADC module state (on/off):

• 1 – turn on the ADC module. The C.1, C.2, C.5, C.6 and B.3 pins become analog inputs (ADC channels). GPIO_GET_CFG and GPIO_GET_PIN_CFG commands will return GPIO_CFG_ADC (0x4) value for the pins. The pins can be used only by the ADC module;

• 0 – turn off the ADC module. The ADC mode will be switched off on the C.1, C.2, C.5, C.6 and B.3 pins. GPIO_GET_CFG and GPIO_GET_PIN_CFG commands will return GPIO_CFG_NOT_CONFIGURED (0xf) value for the pins. The pins can be used by any module.

Byte 3: VREF

This byte contains reference voltage configuration. You can use either USB-I/O adapter supply voltage (V_DD and V_SS) or the external reference voltage connected to C.6 (V_RefHi) and C.5 (V_RefLow) pins:

Bits 7..2	Bit 1	Bit 0
Reserved	VREF_LOW	VREF_HI

Bits 7..2: Reserved

These bits are reserved for future usage and must be set to 0.

Bit 1: VREF_LOW

The low reference voltage:

• 1 – the external voltage reference on C.5 pin is used as low reference voltage;

• 0 – the USB-I/O adapter negative supply voltage (V_SS) is used as low reference voltage.

Bit 0: VREF_HI

The high reference voltage:

• 1 – the external voltage reference on C.6 pin is used as high reference voltage;

• 0 – the USB-I/O adapter positive supply voltage (V_DD) is used as high reference voltage.

If you use the external reference voltage, the following requirements must be met:

• (V_RefHi – V_RefLow) ≥ 3V

• V_SS < V_RefHi < V_DD

• (V_SS – 0.3V) < V_RefLow < (V_DD – 3.0V)

• Impedance of the reference voltage source must be less then 2.5k

Byte 4: RESET_CHANNELS

The ADC channels Reset byte:

• 1 – the ADC channels settings (configured with GPIO_SET_ADC_CHANNEL_CFG command) will be reset. The default values will be applied to all ADC channels;

• 0 – the ADC channels settings (configured with GPIO_SET_ADC_CHANNEL_CFG command and saved in USB-I/O adapter memory) will not be reset.

Bytes 5..7: Reserved

These bytes are reserved for future and must be set to 0.

Response is an 8-byte array of the following format:

Byte 0: GPIO_SET_ADC_MODULE_CFG (0x20)

Response ID (response type). This byte will contain 0x20.

Byte 1: ECHO

Echo byte copied from the corresponding command. It is used to associate the response with the specific command.

Byte 2: ST

Status of the command execution:

Bytes 3..7: Reserved

These bytes are reserved for future usage.