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

Byte 0: GPIO_SET_FR_CNT_CFG (0x16)

This byte contains command ID (command type). It should be set to 0x16.

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:

Bits 7..4	Bits 3..0
ON	FR_CNT_NUMBER

Bits 7..4: ON

The frequency counter state (on/off):

• 1 – the pin will be switched to the frequency counter mode. GPIO_GET_CFG and GPIO_GET_PIN_CFG commands will return GPIO_CFG_FR_CNT (0x6) value for the pin. The pin can be used only by the frequency counter module;

• 0 – the frequency counter mode will be switched off on the pin. GPIO_GET_CFG and GPIO_GET_PIN_CFG commands will return GPIO_CFG_NOT_CONFIGURED (0xf) value for the pin. The pin can be used by any module.

Bits 3..0: FR_CNT_NUMBER

The ID number of the frequency counter:

• 0 – frequency counter on A.3 pin;

• 1 – frequency counter on A.4 pin.

Byte 3: REPEAT

This byte defines the repeat interval in units of 100 ms for the event GPIO_EV_FR_CNT generation. If this byte is non-zero, GPIO-24 adapter sends events each REPEAT*100 ms. For more detailed information see Section 10.1, “Frequency Counter Event”.

Bytes 4..6: COMP_VAL

The threshold frequency to be compared with. The counter calculates frequency and constantly compares it with the threshold frequency specified in Bytes 4..6: COMP_VAL.

Byte 4: COMP_VAL[2] – least significant byte (low byte) of threshold frequency.

Byte 5: COMP_VAL[1] – middle byte of threshold frequency.

Byte 6: COMP_VAL[0] – most significant byte (high byte) of threshold frequency.

Frequency is specified in Hz in the range from 0 to 5,000,000 Hz (5 MHz).

Byte 7: EVENT_COND

The condition of the comparison:

• GPIO_FR_CNT_EV_NONE (0x00) – No events are sent by current frequency counter.

• GPIO_FR_CNT_EV_BELOW (0x01) – Events are sent when the frequency is lower than the threshold value specified in Bytes 4..6: COMP_VAL.

• GPIO_FR_CNT_EV_NOT_EQ (0x02) – Events are sent when the frequency is lower or higher than the threshold value specified in Bytes 4..6: COMP_VAL.

• GPIO_FR_CNT_EV_EQ (0x03) – Events are sent when the frequency is equal to the threshold value specified in Bytes 4..6: COMP_VAL.

• GPIO_FR_CNT_EV_ABOVE (0x04) – Events are sent when the frequency is higher than the threshold value specified in Bytes 4..6: COMP_VAL.

• GPIO_FR_CNT_EV_ALWAYS (0x05) – Events are sent periodically with predefined interval specified in Byte 3: REPEAT.

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

Byte 0: GPIO_SET_FR_CNT_CFG(0x16)

Response ID (response type). This byte will contain 0x16.

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:

• GPIO_ST_SUCCESS (0x00) – Frequency counter was succesfully configured;

• GPIO_ST_INVALID_FR_CNT_NUMBER (0x0A) – Invalid frequency counter ID has been specified (only 1 and 0 are valid);

• GPIO_ST_UNKNOWN_EVENT_TYPE (0x0B) – Unsupported comparison condition has been specified.

Bytes 3..7: Reserved

These bytes are reserved for future usage.