Idiomatic Zener

Prescriptive style rules for .zen code. These apply to all modules, reference designs, and board files.

No Conditional Instantiation

Never use if to create or remove components. Always instantiate every component. Use dnp= to control whether it is populated. This applies to modules, boards, and reference designs, including optional feature blocks.

# BAD
if add_decoupling:
    Capacitor(name="C_VDD", value="100nF", package="0402", P1=VCC, P2=GND)

# GOOD
Capacitor(name="C_VDD", value="100nF", package="0402", P1=VCC, P2=GND)

DNP via Record Pattern

For optional subcircuits controlled by a config, use a record to pair values with DNP state. A zero/disabled config value means dnp=True with placeholder values.

Passive = record(value=typing.Any, dnp=bool)

input_filter = config("input_filter", Frequency, default="0Hz", optional=True,
    help="Input lowpass cutoff. 0Hz disables the filter.")

def input_rc(f):
    dnp = f <= Frequency("0Hz")
    r = e96(Resistance("100ohm") if not dnp else Resistance("0ohm"))
    c = e24(1 / (2 * PI * r * f) if not dnp else Capacitance("100pF"))
    return Passive(value=r, dnp=False), Passive(value=c, dnp=dnp)

input_r, input_c = input_rc(input_filter)
Resistor(name="R_IN", value=input_r.value, dnp=input_r.dnp, package="0402", P1=A, P2=B)
Capacitor(name="C_IN", value=input_c.value, dnp=input_c.dnp, package="0402", P1=B, P2=GND)

Minimize Component Count

Fewer parts = simpler BOM, easier assembly, lower cost.

Prefer value-switching over duplicate components. When a config selects between discrete options, use a single component with a computed value — don't instantiate multiple components with opposing DNP conditions.

# BAD: two resistors, one always DNP
Resistor(name="R_STRAP_HI", value="10kohm", P1=STRAP, P2=VCC, dnp=mode != "HIGH")
Resistor(name="R_STRAP_LO", value="100kohm", P1=STRAP, P2=VCC, dnp=mode != "LOW")

# GOOD: one resistor, value changes with config
_strap_value = { Mode("HIGH"): "10kohm", Mode("LOW"): "100kohm", Mode("FLOAT"): "10kohm" }[mode]
Resistor(name="R_STRAP", value=_strap_value, P1=STRAP, P2=VCC, dnp=mode == Mode("FLOAT"))

Leverage internal pull-ups/pull-downs. Many ICs have internal bias on strap pins. If the default state uses the internal pull, don't add an external resistor — just DNP the single resistor for that case.

Typed Unit Configs

Use physical types from @stdlib/units.zen for configs. Expose one meaningful parameter (e.g. cutoff frequency), not raw R/C values. Use enum() only for discrete design choices.

# BAD
config("filter_r", str, default="10ohms")

# GOOD
input_filter = config("input_filter", Frequency, default="0Hz", optional=True,
    help="Input lowpass cutoff. 0Hz disables the filter.")

Computation in Named Functions

Put calculations in named functions with datasheet references. Snap to E-series with e96() / e24().

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))

Voltage Checks on Power IOs

Every Power io gets voltage_within matching the datasheet's absolute maximum or recommended operating range.

VCC = io("VCC", Power, checks=voltage_within("2.7V to 36V"))

Help Strings

Use help= when it adds integrator-visible meaning that is not already obvious from the name, type, checks, or default. Omit it when it would just restate those fields.

VDD = io("VDD", Power, checks=voltage_within("3.0V to 5.5V"))
GND = io("GND", Ground)
EN = io("EN", Net, help="High to enable the regulator")
input_filter = config("input_filter", Frequency, default="0Hz", optional=True,
    help="Input lowpass cutoff. 0Hz disables the filter.")

No .NET Accessor

Use Power/Ground ios directly as pin connections. Never use .NET.

# BAD
Capacitor(name="C_VDD", value="100nF", P1=VCC.NET, P2=GND.NET)

# GOOD
Capacitor(name="C_VDD", value="100nF", P1=VCC, P2=GND)

Naming

Beyond the standard conventions (UPPERCASE io, lowercase config):

Element	Convention	Example
Internal nets	_ prefix	_VREF, _XI, _RBIAS
Component names	Uppercase functional prefix	R_LOAD, C_VDD, U_LDO
Differential pairs	_P / _N suffixes	IN_P, IN_N (not _PLUS / _MINUS)

Opinionated Defaults

Don't expose configs for implementation details integrators shouldn't tune: decoupling cap values, passive package sizes, test point style.

Do expose configs for things integrators legitimately need to change: filter cutoffs, output voltage, gain settings, enable/disable optional subcircuits.

Checklist

1. No if guards on instantiation — always instantiate, use dnp=
2. No .NET accessor — use ios directly
3. No str configs for physical values — use typed units
4. Calculations in named functions with e96() / e24()
5. voltage_within on all Power ios
6. Add help= only when it clarifies non-obvious integrator-facing meaning
7. Diff pairs use _P / _N, not _PLUS / _MINUS
8. Internal nets prefixed with _
9. Minimize component count — value-switch, leverage internal bias
10. When renaming components or nets, keep existing # pcb:sch comments in sync