Zener Language

Zener Language

Canonical Zener HDL semantics and authoring guidance.

Workflow

1. Use pcb doc --package @stdlib or pcb doc --package <package> to find the public API and source root (<!-- source: ... -->); add --list for the file tree. Read source from that root for exact behavior.
2. Preserve # pcb:sch ... comments; see "Schematic Position Comments" below.
3. After adding, removing, or changing package Module() / load() imports, run pcb sync from the relevant workspace or package, then run pcb build <path> to validate. pcb sync is the dependency reconciliation step; pcb build is the validation step.
4. For recent Zener, stdlib, and pcb CLI changes, check the pcb changelog entries for the installed version and nearby previous releases: https://github.com/diodeinc/pcb/blob/main/CHANGELOG.md

Language

Base language is normal Starlark — expressions, functions, loops, comprehensions, dicts, lists, load(). Below is the Zener-specific layer.

Modules:

• A .zen file is either a normal Starlark module loaded with load() or an instantiable schematic module loaded with Module().
• load("./foo.zen", "helper") imports Starlark symbols. Foo = Module("./Foo.zen") or Foo = Module("github.com/org/repo/path/Foo.zen") loads a subcircuit.
• ./ paths are relative to the current file and resolve within the same package. Cross-package load() and Module() require the full package URL.
• Instantiation always passes name=... first, then any io() / config() inputs. Useful extras: properties, dnp, schematic.

Nets and interfaces:

• Net(name=None, voltage=None, impedance=None) is the base connection type.
• Power, Ground, and NotConnected are specialized net types; more specialized net types live in stdlib.
• Across io() boundaries: NotConnected can promote to any net type; specialized nets can demote to plain Net; plain Net does not auto-promote to specialized types. Use explicit casts like Power(net, voltage=...) or Net(power_net) when needed.

Components and sourcing:

• Component(...) is the primitive physical-part constructor. Required fields are effectively name, symbol, and pins.
• The symbol is the source of truth for footprint, part metadata, and datasheet metadata. Make the symbol properties correct; do not repeat footprint=, part=, or datasheet= in Component() when they are already provided by the symbol.
• Prefer part=Part(mpn=..., manufacturer=...) over legacy scalar mpn and manufacturer when part metadata is not already in the symbol.
• Symbol(library, name=None) points at a .kicad_sym; name is required for multi-symbol libraries.
• Omit no_connect pins from pins; Component() wires NotConnected() automatically.

io():

• Preferred form: flat top-level NAME = io(template, ...) where template is a net/interface type or instance, e.g. Power(voltage="3.3V").
• Do not introduce Pins = struct(...) wrappers for component pins; that older style is deprecated. Existing packages may still use it, but new and touched .zen should expose pins as top-level io()s.
• Name is inferred from the assignment target. optional=True means omitted inputs get auto-generated nets or interfaces.

config():

• Preferred form: name = config(typ, default=..., ...); name is inferred from the assignment target.
• typ can be primitive types, enums, records, or physical values such as Voltage, Current, or Resistance.
• Use physical types from @stdlib/units.zen for every physical-value config, even when only a few choices are valid. Constrain discrete choices with allowed=[...]; strings auto-convert, e.g. config(Current, default="3A", allowed=["1A", "2A", "3A"]).
• Use enum() only for non-physical design choices such as operating mode, protocol variant, polarity, or enablement strategy.

Public compatibility:

• For reusable packages, compatibility means existing consumers can update without changing their Zener, layout, or integration assumptions.
• Breaking changes include public interface changes (io(), config(), entrypoints, module call shape), substantial layout/physical integration changes, or behavior changes that require consumer action. Collapsing loose ios into one interface is breaking even if the netlist still builds.
• pcb build passing only validates the current package; it does not prove existing consumers remain compatible. When making a breaking change, document the migration and mark the commit as breaking.

Utilities:

• Layout(name, path) associates reusable layout metadata to a module.
• check(condition, message), warn(message), and error(message) are the validation and diagnostic primitives.

Authoring Idioms

Power, Interfaces, And Checks

• Keep rails explicit with prelude Power(voltage=...) and Ground; each public Power io() declares its voltage range unless the local API intentionally keeps it generic.
• Use @stdlib/interfaces.zen interfaces for buses and grouped signals that are not in the prelude; prefer public bus interfaces such as I2c, Spi, Qspi, Uart, Usb2, or DiffPair over separate loose top-level nets when the grouped signal semantics are clear.
• Use typed values and validation primitives (check(...), warn(...), error(...), @stdlib/checks.zen) for electrical constraints instead of comments when possible.
• Connect Power and Ground ios directly to pins and passives.

VDD = io(Power(voltage="3.0V to 5.5V"))
GND = io(Ground)
EN = io(Net, help="High to enable the regulator")

Configs And Computation

• Expose meaningful design choices, not incidental implementation details. Good configs include output voltage, gain, cutoff frequency, address, mode, or optional feature enablement. Avoid configs for fixed decoupling values, passive package sizes, and test-point style unless local code already makes them public API.
• Prefer one meaningful physical config over raw R/C/L strings. For example, expose a cutoff Frequency and compute snapped passives internally.
• Put non-trivial calculations in named functions with datasheet section or equation references when available. Snap results to E-series values with e96(), e24(), or the appropriate stdlib utility.

def load_r(v_out, v_sense):
    """Datasheet §8.1.1 / Eq 4: V_OUT = V_SENSE × gm × R_L"""
    GM = Current("200uA") / Voltage("1V")
    return e96(v_out / (v_sense * GM))

DNP And Optional Circuitry

• Configs may change component values and dnp= state, but they should not change which instances or nets exist in the schematic.
• Never use conditional instantiation to add, remove, or reconnect circuitry. Always instantiate the relevant components and use dnp= for population state.
• When a config selects a value on the same two nets, prefer one component with a computed value.
• When a config selects between mutually exclusive net straps, instantiate each strap option and DNP the inactive ones so topology stays stable.
• Leverage an IC's internal pull-up or pull-down when the default mode uses it; use external bias components with dnp= only for populated alternatives.

load("@stdlib/units.zen", "Voltage", "Resistance")
load("@stdlib/utils.zen", "e96")

Resistor = Module("@stdlib/generics/Resistor.zen")

Mode = enum("PFM", "PWM")
mode = config(Mode, default="PFM")
voltage_out = config(Voltage, default="5V", allowed=["3.3V", "5V"])

VOUT = io(Power(voltage=voltage_out))
GND = io(Ground())

VFB_REF = Voltage("0.8V")
R_FB_TOP_VAL = Resistance("100kohm")

def fb_bottom(vout):
    """Datasheet Table 1: R2 = R1 × VFB / (VOUT − VFB)"""
    return e96(R_FB_TOP_VAL * VFB_REF / (vout - VFB_REF))

VCC = Power()
FB = Net()
MSYNC = Net()

# Same feedback divider instances and nets for every output voltage; only value changes.
Resistor(name="R_FB_TOP", value=R_FB_TOP_VAL.with_tolerance("1%"), package="0402", P1=VOUT, P2=FB)
Resistor(name="R_FB_BOT", value=fb_bottom(voltage_out).with_tolerance("1%"), package="0402", P1=FB, P2=GND)

# Same strap options and nets for every mode; only population changes.
Resistor(name="R_MSYNC_GND", value="0ohm", package="0402", P1=MSYNC, P2=GND, dnp=mode != Mode("PFM"))
Resistor(name="R_MSYNC_VCC", value="0ohm", package="0402", P1=MSYNC, P2=VCC, dnp=mode != Mode("PWM"))

Style

• Prefer concise one-line io() and config() declarations when readable.
• Avoid overly verbose help= text. Use help= only when it adds integrator-visible meaning that is not already obvious from the name, type, or default.
• Omit comments and help text that merely restate the code.
• Do not use decorative section-divider comments such as # ===== Config =====, # ----- IOs -----, or multi-line banner blocks. They add no value.
• These comment-cleanup rules never apply to # pcb:sch lines; see "Schematic Position Comments".

Naming

Schematic Position Comments (# pcb:sch)

Schematic placement is stored in # pcb:sch <ID> x=... y=... rot=... comments at the end of a .zen file. Treat existing records as persisted layout state, not as ordinary comments.

• Preserve existing placement records through textual Zener edits. Add new code above the block.
• When renaming a component or net, update the matching names inside its records. When deleting a component, remove only its own records.
• Do not add records for new components, edit coordinates by hand, or otherwise change placement unless the user explicitly asks for schematic layout changes. Schematic editor/MCP layout operations may update these records as part of layout persistence. Unpositioned new items may be displayed with auto-placement, but that does not make existing placement records disposable.

Packages And Manifests

Imports and dependencies:

• @stdlib/... is implicit and toolchain-managed; do not declare it in [dependencies].
• Package imports in .zen use full package URLs without versions.
• Do not manually edit pcb.toml to add or remove package dependencies. Add or remove the Module() / load() import in .zen, then run pcb sync.
• pcb sync updates package manifests: [dependencies] for direct package imports and [dependencies.indirect] for the resolved transitive dependency state.
• Let pcb sync maintain pcb.toml, especially [dependencies.indirect]. Commit pcb.toml files after pcb sync changes them.

Updating dependency versions:

• Run dependency update commands from the package directory.
• pcb list -m -u is read-only. It shows direct remote dependencies, the latest compatible update in brackets, and the latest breaking update as [breaking: ...].
• pcb add -u updates all direct remote dependencies to the latest stable compatible version; pcb add -u <url> updates one.
• For a specific or breaking version, check versions with pcb list -m -versions <url>, then run pcb add <url>@<version>. Do not edit pcb.toml.
• Do not use pcb update; it is for legacy dependency manifests.

pcb.toml per repository/package type:

• Board repository root: [workspace] metadata, [board] with name, path, and description, and board [dependencies].
• Registry repository root: [workspace] metadata and top-level components/** / modules/* members; no [board].
• Reusable packages (modules, components): [dependencies] and optional default parts.

Stdlib

Prelude symbols available in .zen files without load(): Net, Power, Ground, NotConnected, Board, Layout, Part. Local definitions can shadow them.

@stdlib/board_config.zen:

• Board is a prelude helper backed by @stdlib/board_config.zen. For standard boards, prefer the layers= helper instead of manually writing stackups and design rules:

  Board(name="MainBoard", layout_path="layout/MainBoard", layers=4)
  

• layers selects default stackup, netclasses, constraints, and predefined sizes for common 2/4/6/8/10-layer boards.

• outer_copper_weight, copper_finish, solder_mask_color, track_widths, and via_dimensions customize those defaults. Extra track widths and vias are appended, deduplicated, and sorted.

• Use explicit BoardConfig, Stackup, DesignRules, NetClass, and related records only when the standard defaults are insufficient; if both layers and config are provided, config is merged over the layers-derived defaults.

@stdlib/interfaces.zen:

• Common interfaces: DiffPair, I2c, I3c, Spi, Qspi, Uart, Usart, Swd, Jtag, Usb2, Usb3, and others.
• UartPair() and UsartPair() generate cross-connected point-to-point links.

@stdlib/units.zen:

• Physical types: Voltage, Current, Resistance, Capacitance, Inductance, Impedance, Frequency, Temperature, Time, Power.

• Constructors accept point values and ranges:

  Voltage("3.3V")             # point value
  Resistance("4k7")           # 4.7kΩ resistor notation
  Capacitance("100nF")
  Voltage("1.1–3.6V")          # range
  Voltage("11–26V (12V)")      # range with explicit nominal
  

• Arithmetic tracks units automatically: Voltage("3.3V") * Current("0.5A") → 1.65W; Voltage("5V") / Current("100mA") → 50Ω.

• Properties: .value (alias for .nominal), .nominal, .min, .max, .tolerance, .unit.

• Methods: .with_tolerance(t), .with_value(v), .with_unit(u), .abs(), .diff(other), .within(other), .matches(other).

• Operators: +, -, *, / (with unit tracking), <, >, <=, >=, == (strict equality against another PhysicalValue), unary -. Use .matches(other) for coercive comparisons against strings or scalars, e.g. Voltage("5V").matches("5V").

• String formatting: point → "3.3V"; symmetric tolerance → "10k 5%"; range → "11–26V (16V nom.)".

@stdlib/checks.zen:

• voltage_within(...) is the main reusable io()-boundary power-rail check.

@stdlib/utils.zen:

• e3, e6, e12, e24, e48, e96, e192 snap physical values to standard E-series.

@stdlib/generics/*:

• Prefer generics for common parts: Resistor, Capacitor, Inductor, FerriteBead, Led, Rectifier, Zener, Tvs, Crystal, TestPoint, PinHeader, NetTie, SolderJumper, MountingHole, Fiducial, Version.
• Diode is deprecated; use Rectifier (standard/Schottky), Zener (breakdown/reference), or Tvs (transient suppressor).