Universal Tools

These 8 tools work with any pyvisa backend — AR488, pyvisa-py, NI-VISA, or simulation. They cover backend lifecycle management, instrument discovery, and standard SCPI communication. A backend must be connected before instruments on it can be accessed.

Instruments are addressed by VISA resource string ("GPIB0::22::INSTR") or by a configured alias ("dmm"). Aliases are resolved through the [instruments] section of mcpyvisa.toml.

---

server_status

Returns the current state of all configured backends (connected or not), discovered instruments, and the server version. This is the first tool to call when starting a session.

Parameters

This tool takes no parameters.

Example

result = await client.call_tool("server_status", {})

Returns

mcpyvisa v0.1.0

Backends:
  bench-a: ar488 serial (/dev/ttyUSB0) [connected]
  lan: pyvisa-py [disconnected]

Instruments:
  GPIB0::5::INSTR — Agilent Technologies E3631A (alias: psu)
  GPIB0::22::INSTR — KEITHLEY INSTRUMENTS INC. MODEL 2000 (alias: dmm)

---

connect_backend

Connect to a backend and initialize it. For AR488 backends, this establishes serial or TCP communication and runs the AR488 initialization sequence. For pyvisa-py or system backends, this creates a pyvisa ResourceManager with the appropriate VISA library.

If auto_discover is enabled in the backend config, instruments are discovered immediately after connecting. If auto_identify is also enabled, *IDN? is sent to each discovered instrument.

AR488 initialization sequence

For AR488 backends, the adapter is configured for machine-parseable output:

1. ++verbose 0 — numeric responses only
2. ++prompt 0 — suppress command prompt
3. ++auto 0 — manual read mode
4. ++mode 1 — controller mode
5. ++eoi 1 — assert EOI on last byte
6. ++eos 0 — append CR+LF to writes
7. ++read_tmo_ms — set configured timeout
8. ++ver — verify communication

Parameters

Name	Type	Required	Description
backend	string	Yes	Name of the backend to connect

Example

result = await client.call_tool("connect_backend", {
    "backend": "bench-a"
})

Returns

Connected to bench-a (ar488 via /dev/ttyUSB0)
Discovered 2 instrument(s):
  GPIB0::5::INSTR — Agilent Technologies E3631A
  GPIB0::22::INSTR — KEITHLEY INSTRUMENTS INC. MODEL 2000

Connection failures

If connection fails, check:

• AR488 serial: Is the USB cable connected? Is the serial port path correct? Is another process holding the port?
• AR488 TCP: Is the ESP32 powered and connected to WiFi? Is the IP address correct? The ESP32 allows only one TCP client at a time.
• pyvisa-py: Is pyvisa-py installed? Are USB-TMC devices connected?
• System VISA: Is NI-VISA or Keysight IO Libraries installed?

---

disconnect_backend

Disconnect from a backend. Closes all underlying transport connections. Instruments on the bus return to local control.

Parameters

Name	Type	Required	Description
backend	string	Yes	Name of the backend to disconnect

Example

result = await client.call_tool("disconnect_backend", {
    "backend": "bench-a"
})

Returns

Disconnected from bench-a

---

discover_instruments

Scan a backend for connected instruments. On GPIB backends, this sends ++findlstn to discover all listeners, then optionally sends *IDN? to each. On non-GPIB backends, this calls list_resources() to find connected instruments.

Parameters

Name	Type	Required	Description
backend	string	Yes	Name of the backend to scan

Example

result = await client.call_tool("discover_instruments", {
    "backend": "bench-a"
})

Returns

Discovered 3 instrument(s) on bench-a:
  GPIB0::5::INSTR — Agilent Technologies E3631A
  GPIB0::7::INSTR — Tektronix TDS2024B
  GPIB0::22::INSTR — KEITHLEY INSTRUMENTS INC. MODEL 2000

Tip

On GPIB backends, discovery runs ++findlstn and sends *IDN? to each listener. For faster scans when you only need to know which addresses are active, older instruments that do not support *IDN? will show as unidentified.

---

instrument_query

Send a query to an instrument and return the response. This is the most common operation — send a command (typically ending with ?) and read back the instrument’s answer.

Parameters

Name	Type	Required	Description
instrument	string	Yes	VISA resource string or configured alias
command	string	Yes	Command to send (typically ends with ?)

Example

# Query by alias
result = await client.call_tool("instrument_query", {
    "instrument": "dmm",
    "command": "MEAS:VOLT:DC?"
})

# Query by VISA resource string
result = await client.call_tool("instrument_query", {
    "instrument": "GPIB0::22::INSTR",
    "command": "MEAS:VOLT:DC?"
})

# Check operation complete
result = await client.call_tool("instrument_query", {
    "instrument": "psu",
    "command": "*OPC?"
})

Returns

The raw response string from the instrument, for example:

+4.23451000E+00

Note

If the instrument does not respond within the configured read_timeout_ms, an error is raised. Increase the backend timeout with configure_ar488 for slow measurements (e.g., high-resolution ADC integrations).

---

instrument_write

Send a command to an instrument with no response expected. Use this for configuration commands that set parameters without returning data.

Parameters

Name	Type	Required	Description
instrument	string	Yes	VISA resource string or configured alias
command	string	Yes	Command to send

Example

# Configure a Keithley 2000 for DC voltage measurement
await client.call_tool("instrument_write", {
    "instrument": "dmm",
    "command": "CONF:VOLT:DC 10,0.001"
})

# Turn on output on a power supply
await client.call_tool("instrument_write", {
    "instrument": "psu",
    "command": "OUTP ON"
})

# Using a VISA resource string directly
await client.call_tool("instrument_write", {
    "instrument": "GPIB0::9::INSTR",
    "command": "TRIG:SOUR IMM"
})

Returns

Sent to dmm: CONF:VOLT:DC 10,0.001

---

instrument_identify

Identify an instrument by sending the IEEE 488.2 *IDN? query. The response is parsed into four fields per the standard: manufacturer, model, serial number, and firmware version.

Parameters

Name	Type	Required	Description
instrument	string	Yes	VISA resource string or configured alias

Example

result = await client.call_tool("instrument_identify", {
    "instrument": "dmm"
})

Returns

dmm (GPIB0::22::INSTR):
  Manufacturer: KEITHLEY INSTRUMENTS INC.
  Model: MODEL 2000
  Serial: 1234567
  Firmware: A01
  Raw: KEITHLEY INSTRUMENTS INC.,MODEL 2000,1234567,A01

Caution

Older instruments (HP 3478A, Fluke 8842A, etc.) may not support *IDN? at all. These pre-IEEE-488.2 instruments will time out. Use discover_instruments to find them, then refer to the instrument’s programming manual for command syntax.

---

instrument_reset

Send *RST to reset an instrument to its power-on defaults. This clears all configuration and returns the instrument to a known state.

Parameters

Name	Type	Required	Description
instrument	string	Yes	VISA resource string or configured alias

Example

result = await client.call_tool("instrument_reset", {
    "instrument": "dmm"
})

Returns

Reset instrument dmm (GPIB0::22::INSTR)

Tip

After *RST, most instruments need a brief settling period (a few hundred milliseconds to a few seconds depending on the model) before they accept new configuration commands. Some instruments support *OPC? to signal readiness.