CIRCUIT URL

Paste a GitHub raw JSON link, a github.com file page, or a path on this site (e.g. 7seg_answer_circuit.logiclab.json).

LogicLab — quick help

• Place a part: click it in the left panel, then click the sheet. Shift-click to place several.
• Wire: drag from an output lead to an input lead. One wire per input. While wiring, click on the sheet to add intermediate line bends.
• Rotate: select a component and click the rotate button or press R to turn it 90°.
• Zoom: scroll the mouse wheel over the sheet to zoom in/out. FIT (or double-click / double-tap empty space) zooms to the whole circuit. On touch screens: drag empty space to pan, pinch to zoom, tap a live switch to toggle it. Editing works too: tap a palette part then tap the sheet to place it, drag parts to move them, tap an output pin then an input pin to wire (tap empty space for bend points, double-tap to cancel).
• Pan: drag on an empty part of the sheet (or use the middle mouse button). A plain click on empty space clears the selection.
• Power: energize the circuit. Wires turn green for 1, grey for 0.
• Inputs: click an IN switch to toggle it — at any moment, including mid clock-cycle. (Double-click to rename it while the power is off.)
• Logic 1 / Logic 0: fixed sources that always drive a constant high or low — wire them into any input.
• Clock: the CLK part runs automatically; set speed with the slider. Pause (❚❚) stops it; STEP then advances one full clock cycle (rising edge to rising edge) at a time.
• Flip-flops sample their inputs on the rising clock edge.
• LUT4: a 4-input / 1-output lookup table. Double-click it to set the 16-bit truth table as hex (e.g. 0x0FF0). Output = bit n of that value, where n = I3 I2 I1 I0 and I0 is the LSB.
• 7-SEG display: one active-high input per segment (a top, then b..f clockwise, g middle) — drive it from your own decoder built from gates, LUT4s, or a ROM programmed with the segment font (see the counter example).
• Bus blocks: every multi-bit port is broken into single-bit pins, LSB first (A0 is the least significant). Wire one bit per pin. When powered, each block shows a live value readout on its face.
• MUX 2:1: Y = S ? I1 : I0. Decoder 4:16: exactly one of Y0..Y15 is high, selected by the address (n = A3 A2 A1 A0, A0 the LSB). ALU 4-bit: M=0 computes A+B, M=1 computes A-B (as A + ~B + 1); Co is the carry out of bit 3 (on subtract, Co=1 means no borrow, i.e. A ≥ B).
• Register 4-bit: on the rising clock edge it loads D0..D3 into Q0..Q3 when EN is high, otherwise it holds its value. Counter 4-bit: a free-running up counter that increments on every rising clock edge and wraps from 15 back to 0.
• ROM 16x8 / RAM 16x8: 4-bit address A0..A3, 8-bit data. Reads are combinational (the addressed byte is always present on the outputs). RAM writes D0..D7 into the addressed cell on the rising clock edge when WE (write enable) is high. Double-click either block to edit its contents as 16 hex bytes (address 0 first).
• Move / delete: drag a part to move; select it (or a wire) and press Delete. Esc cancels.
• Timing panel traces clocks, inputs, flip-flop Q and outputs over time.
• Save / Open: SAVE downloads the circuit as a .json file; OPEN loads one back.
• URL: opens a dialog to load a circuit straight from a link, and to create share links. Use a GitHub raw link (raw.githubusercontent.com/...) or a path on this site; a normal github.com file page is converted automatically. Copy share link turns the entered URL into a ?circuit=<url> link that opens the circuit directly; after loading, the address bar shows the same link.