Analysis of Some HART commands

We know about the HART protocol. This time we will summarize Part Of The HART command. Hope to help you. For more information, see the article.

HART command 0: read ID code

Return the extended device type code, version, and device ID code ｡

Request: None
Response:
Bytes: 0: 254
Byte 1: Manufacturer ID
Byte 2: Manufacturer device type
Byte 3: Number of request headers
Byte 4: General Command document version number
Byte 5: Specification version number of the transmitter
Byte 6: Device Software Version Number
Byte 7: Device hardware version number
Byte 8: device identifier
Byte 9-11: device ID

HART command 1: Read main variable (PV)

Return the value of the primary variable as a floating point ｡

Request: None
Response:
Byte 0: Master variable unit code
Byte 1-4: primary variable

HART command 2: Read the main variable current value and percentage

Read the main variable current and percentage. The main variable current always matches the AO output current of the device. The percentage is not limited to 0-100%. If the percentage exceeds the main variable range, the upper and lower limits of the sensor are tracked ｡

Request: None
Response:
Byte 0-3: Active Variable current, in the unit
Byte 4-7: Percentage of the main variable range

HART command 3: Read the dynamic variable and main variable current

Read the main variable current and four (up to) predefined dynamic variables. The main variable current always matches the AO output current of the device. The second, third, and fourth variables are defined for each device type, for example, the second variable is the sensor temperature ｡

Request: None
Response:
Byte 0-3: Active Variable current, in the unit
Byte 4: Master variable unit code
5-8 Bytes: primary variable
Byte 9: second variable unit code
Byte 10-13: second variable
Byte 14: third variable unit code
Byte 15-18: third variable
Byte 19: Fourth variable unit code
Byte 20-23: Fourth variable

HART command 4: retain

HART command 5: retain

HART Command 6: Write the POLLING address

This is the data link layer management command. This command writes the Polling address to the device, which is used to control the main variable AO output and provide the device ID ｡

Only when the device's Polling address is set to 0 Can the device's main variable AO be output. if the address is 1 ~ 15 then the AO is not active and does not respond to the application process. At this time, the AO is set to the minimum, and the third digit of the transmission status is set-the master variable analog output is fixed; the upper/lower limit alarm is invalid. If the Polling address is changed back to 0, the main variable AO is active again and can respond to the application process ｡

Request:
Byte 0: the device's Polling address
Response:
Byte 0: the device's Polling address