Modbus devices#
According to gateway specification, all modbus device event types have prefix:
'gateway', <gateway_name>, 'modbus_master', <device_name>, <source>, ...
Together with modbus specific events, generic enable and running events are also supported.
Modbus specific events don’t contain source_timestamp.
Data value#
All modbus native data types are encoded as 1bit or 16bit addressable values. Because of different data encoding schemas, single user defined data values can occupy only parts of modbus registers or span across multiple registers. To accommodate these different encoding rules, modbus gateway devices represent single data point values as list of bits, encoded as single unsigned integer, with legth specified by configuration parameters.
Among other parameters, each data specifies:
data type (1bit or 16bit register size)
bit count
starting register address
bit offset
List of bit values is created by iterative reading of register values starting with starting register address and incrementing register address by 1. Bits in each register are read starting with most significant and advancing to the least significant bit. Starting register bit defines bit offset - number of bits which are skipped during start of this iterative procedure. These skipped bits are not included in resulting value and are not taken into account in bit count calculation.
Encoding/decoding example#
In case of 16bit registers with content:
Address
Value
1000
0x1234
1001
0x5678
1002
0x9abc
When data item is configured with properties:
bit count: 32
starting register address: 1000
bit offset: 8
Data value is unlimited unsigned integer 0x3456789a.
Modbus master#
Modbus master device configuration is specified by
hat-gateway://modbus.yaml#/$defs/master.
Once enabled, modbus master device will try to open communication connection
defined by configuration parameters. While connection is established,
this device repeatedly reads modbus registers (in accordance to configured
polling interval defined for each data in READ direction) and reports
any changes as read responses. Also, received write requests are propagated to
remote devices which result in write responses. If connection is lost or could
not be established, device repeatedly tries to establish new connection after
connect_delay seconds defined in configuration.
Together with read and write processing, device continuously reports current status of communication connection and each modbus device identified by device_id data parameter. Status of modbus device identified by device_id is calculated according to availability of data associated with that device_id. Available remote device statuses:
DISABLEDData polling is not enabled
CONNECTINGData polling is enabled and some data read requests have resulted in timeout or haven’t completed.
CONNECTEDData polling is enabled and all data read responses have been received.
DISCONNECTEDTransitive status signaling transition from
CONNECTEDtoCONNECTING.
Polling of data values can be enabled/disabled based on device_id. Initially, polling for all remote devices is disabled and has to be explicitly enabled.
Gateway events#
Events registered by gateway have event type starting with:
'gateway', <gateway_name>, 'modbus_master', <device_name>, 'gateway', ...
Available gateway events are:
…, ‘status’
Connection status of a modbus master device.
Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/gateway/status.…, ‘remote_device’, <device_id>, ‘status’
Status of a remote modbus device, where <device_id> is remote modbus device identifier device_id defined in configuration for each data.
Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/gateway/remote_device_status.…, ‘remote_device’, <device_id>, ‘read’, <data_name>
Read response reporting current data value. Data value and cause of event reporting are available only in case of successful read. <data_name> is configuration defined name for each data.
First successful read of data value will be reported with
INTERROGATEcause and resultSUCCESS, while all the following successful reads, where value is different from previous are reported withCHANGEcause. If read is not successful, result equals to any other string that indicate reason of failure (value and cause properties are not included). After value is invalidated, next successful read will be reported with INTERROGATED cause.Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/gateway/read.…, ‘remote_device’, <device_id>, ‘write’, <data_name>
Write response reporting resulting success value. Together with result that contains success value, this event contains the same request_id as provided in associated write request event.
Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/gateway/write.Note
in case response did not arrive within configuration defined request_timeout, response with result
TIMEOUTis registered.
System events#
Events registered by other Hat components, which are consumed by gateway, have event type starting with:
'gateway', <gateway_name>, 'modbus_master', <device_name>, 'system', ...
Available system events are:
…, ‘remote_device’, <device_id>, ‘enable’
Enable polling of data associated with remote modbus device with <device_id> identifier.
Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/system/enable.…, ‘remote_device’, <device_id>, ‘write’, <data_name>
Write request containing data value and session identifier used for pairing of request/response messages.
Payload is defined by
hat-gateway://modbus.yaml#/$defs/events/master/system/write.
Configurations and event payloads#
$schema: "https://json-schema.org/draft/2020-12/schema"
$id: "hat-gateway://modbus.yaml"
title: Modbus devices
$defs:
master:
type: object
title: Modbus master
required:
- connection
- remote_devices
properties:
connection:
type: object
required:
- modbus_type
- transport
- connect_timeout
- connect_delay
- request_timeout
- request_delay
- request_retry_immediate_count
- request_retry_delayed_count
- request_retry_delay
properties:
modbus_type:
description: |
Modbus message encoding type
enum:
- TCP
- RTU
- ASCII
transport:
oneOf:
- type: object
required:
- type
- host
- port
properties:
type:
const: TCP
host:
type: string
description: |
Remote host name
port:
type: integer
description: |
Remote host TCP port
default: 502
- type: object
required:
- type
- port
- baudrate
- bytesize
- parity
- stopbits
- flow_control
- silent_interval
properties:
type:
const: SERIAL
port:
type: string
description: |
Serial port name (e.g. /dev/ttyS0)
baudrate:
type: integer
description: |
Baud rate (e.g. 9600)
bytesize:
description: |
Number of data bits
enum:
- FIVEBITS
- SIXBITS
- SEVENBITS
- EIGHTBITS
parity:
description: |
Parity checking
enum:
- NONE
- EVEN
- ODD
- MARK
- SPACE
stopbits:
description: |
Number of stop bits
enum:
- ONE
- ONE_POINT_FIVE
- TWO
flow_control:
type: object
required:
- xonxoff
- rtscts
- dsrdtr
properties:
xonxoff:
type: boolean
description: |
Enable software flow control
rtscts:
type: boolean
description: |
Enable hardware (RTS/CTS) flow control
dsrdtr:
type: boolean
description: |
Enable hardware (DSR/DTR) flow control
silent_interval:
type: number
description: |
Serial communication silet interval
connect_timeout:
type: number
description: |
Maximum number of seconds available to single connection
attempt
connect_delay:
type: number
description: |
Delay (in seconds) between two consecutive connection
establishment attempts
request_timeout:
type: number
description: |
Maximum duration (in seconds) of read or write
request/response exchange.
request_delay:
type: number
description: |
Delay (in seconds) between two consecutive requests
(minimal duration between response and next request)
request_retry_immediate_count:
type: integer
description: |
Number of immediate request retries before remote
data is considered unavailable. Total number
of retries is request_retry_immediate_count *
request_retry_delayed_count.
request_retry_delayed_count:
type: integer
description: |
Number of delayed request retries before remote data
is considered unavailable. Total number
of retries is request_retry_immediate_count *
request_retry_delayed_count.
request_retry_delay:
type: number
description: |
Delay (in seconds) between two consecutive delayed
request retries
remote_devices:
type: array
items:
type: object
required:
- device_id
- timeout_poll_delay
- data
properties:
device_id:
type: integer
description: |
Modbus device identifier
timeout_poll_delay:
type: number
description: |
Delay (in seconds) after read timeout and
before device polling is resumed
data:
type: array
items:
type: object
required:
- name
- interval
- data_type
- start_address
- bit_offset
- bit_count
properties:
name:
type: string
description: |
Data point name
interval:
type:
- number
- "null"
description: |
Polling interval in seconds or
null if polling is disabled
data_type:
description: |
Modbus register type
enum:
- COIL
- DISCRETE_INPUT
- HOLDING_REGISTER
- INPUT_REGISTER
- QUEUE
start_address:
type: integer
description: |
Starting address of modbus register
bit_offset:
type: integer
description: |
Bit offset (number of bits skipped)
bit_count:
type: integer
description: |
Number of bits used for
encoding/decoding value (not
including offset bits)
events:
master:
gateway:
status:
enum:
- DISCONNECTED
- CONNECTING
- CONNECTED
remote_device_status:
enum:
- DISABLED
- CONNECTING
- CONNECTED
- DISCONNECTED
read:
type: object
required:
- result
properties:
result:
enum:
- SUCCESS
- INVALID_FUNCTION_CODE
- INVALID_DATA_ADDRESS
- INVALID_DATA_VALUE
- FUNCTION_ERROR
value:
type: integer
cause:
enum:
- INTERROGATE
- CHANGE
write:
type: object
required:
- request_id
- result
properties:
request_id:
type: string
result:
enum:
- SUCCESS
- INVALID_FUNCTION_CODE
- INVALID_DATA_ADDRESS
- INVALID_DATA_VALUE
- FUNCTION_ERROR
- TIMEOUT
system:
enable:
type: boolean
write:
type: object
required:
- request_id
- value
properties:
request_id:
type: string
value:
type: integer