Run a SPICE DC Operating Point in Cloud#

Save a resistor and DC-source circuit, choose the R/I or R/I/V analysis, and read its node voltages and branch currents.

Overview#

Calculate steady node voltages and branch currents from a saved .cir file. Choose the analysis that matches the elements in your circuit.

Flow Navigator entry	Accepted elements
SPICE DC operating point	Resistors (`R`) and independent DC current sources (`I`)
SPICE DC operating point (R/I/V)	Resistors and independent DC current and voltage sources (`R`, `I`, `V`)

Open a Cloud project with local analysis access. Cloud performs the calculation in your browser. See Digital Design Studio for opening a project. Both analyses read the saved project file; save editor changes before running.

Save the Example Circuit#

Create or open circuits/ohms-law.cir in the project editor, enter the following text, and save the file.

Altifigence authored Ohm's-law circuit
* SPDX-License-Identifier: Apache-2.0
R1 n 0 10
I1 0 n DC 2m
.op
.end

R1 connects node n to ground (0) through 10 Ω. I1 supplies 2 mA from ground to n. The resistor carries 2 mA back to ground, giving V(n) = 0.002 × 10 = 0.02 V.

Run the Saved File#

Open Flow Navigator → Simulation → SPICE DC operating point.
In Saved workspace .cir file, choose or enter circuits/ohms-law.cir.
Click Run DC operating point.
When DC operating point completed appears, compare the tables with the values below.

The path is relative to the open project. It must identify a saved .cir file in that project. If you have edited the selected file, save it before running again. Running an analysis does not save edits or change the circuit file.

Read the R/I Results#

Table	Name	Expected value
Node voltages	`0`	0 V
Node voltages	`n`	0.02 V
Branch currents	`i1`	0.002 A
Branch currents	`r1`	0.002 A

Positive branch current flows from the first terminal to the second terminal on that element’s line. For this circuit, i1 flows from 0 to n, while r1 flows from n to 0. Result names use lowercase letters.

SHA-256 identifies the exact saved input used for that result, including its title and comments.

Add a DC Voltage Source#

Use the separate SPICE DC operating point (R/I/V) entry for voltage sources. Save this example as circuits/supply.cir.

Own RIV DC supply and loaded divider
* SPDX-License-Identifier: Apache-2.0
V1 supply 0 DC 5
R1 supply load 1k
R2 load 0 1k
I1 load 0 DC 1m
.op
.end

Open Flow Navigator → Simulation → SPICE DC operating point (R/I/V).
In Saved workspace .cir file, choose circuits/supply.cir.
Click Run DC operating point and wait for DC operating point completed.

Table	Name	Expected value
Node voltages	`0`	0 V
Node voltages	`load`	2 V
Node voltages	`supply`	5 V
Branch currents	`i1`	0.001 A
Branch currents	`r1`	0.003 A
Branch currents	`r2`	0.002 A
Branch currents	`v1`	-0.003 A

V1 holds supply 5 V above ground. The 1 mA load makes the divider output 2 V. The negative v1 current means current flows opposite to its written terminal order: this source delivers 3 mA to the circuit.

Write Another Circuit#

Use the following forms. The DC keyword is optional for current and voltage sources. Values must be finite; resistance must be positive.

Element	Statement	Value unit
Resistor	`Rname first second resistance`	Ω
Current source	`Iname first second DC current`	A
Voltage source, R/I/V only	`Vname first second DC voltage`	V

Values accept decimal or scientific notation and these case-insensitive suffixes: t, g, meg, k, m, u, n, p, f. Both m and M mean milli; use meg for mega. Write 2m, not 2mA, and 10, not 10ohm. A negative current reverses its direction. A voltage source sets the first terminal’s voltage minus the second terminal’s voltage to its stated value.

The first line is a nonempty title. Use ASCII for the remaining circuit statements, with blank lines or whole-line * comments as needed. Include one .op and finish with .end. Names use case-insensitive letters, digits and underscores, up to 64 characters. Element names begin with R, I, or V as appropriate and contain at least two characters. Connect distinct terminals.

For R/I, every non-ground node needs a resistor path to ground. For R/I/V, that path may use resistors or voltage sources. Voltage-source-only loops and duplicate voltage constraints are rejected because their branch currents cannot be determined uniquely. The R/I entry continues to reject voltage sources.

Capacitors, inductors, transistor or other device models, subcircuits, includes, expressions, AC and transient analyses are not accepted. An unsupported statement stops the whole run.

Check Limits and Residuals#

Input limit	Maximum
Saved file size	64 KiB (65,536 bytes)
Physical lines, including the title	4,096
Nodes, including ground	256
Elements	1,024
R/I/V unknowns: non-ground nodes plus voltage sources	256

The R/I KCL residual measures the remaining current imbalance at non-ground nodes and must be within the displayed accepted limit. The R/I/V panel reports the KCL residual and Voltage constraint residual separately, together with their fixed tolerances. A result appears only when its checks pass.

In R/I/V, IR SHA-256 identifies the canonical circuit. Equivalent element order, letter case and numeric spellings share that identity; SHA-256 still distinguishes the exact saved file bytes.

Cancel or Correct a Run#

Click Cancel to stop an active calculation. Cancelling… remains visible until the operation settles. Run one SPICE DC operation at a time. If shutdown cannot be confirmed, reload the Cloud page before trying again.

For a source diagnostic, click its file-and-line link to open the statement in the editor. Correct it, save, and run again. Solver failures may have no source line; check the circuit’s ground connections and numeric values.

If the file cannot be read, check its saved .cir path, access permissions, and 64 KiB size limit. If a time or resource limit is reached, reduce the circuit before trying again.

Editing the selected file, changing workspace or closing the tab clears the displayed result. Reopening a restored tab does not run the circuit: select the saved file and click Run DC operating point again.