Electronics Stack Output Design Spec

Stack-Output Board (V1.0) Design Specification

Status: Draft Project: Enigma-NG Author: Izzyonstage & GitHub Copilot Version: v.0.1.0 Associated Hardware Revision: Rev A Last Updated: 2026-09-02

1. Overview

The Stack-Output Board is the output-side board of the Rotor Mini-Stack assembly. It fulfils the output-side responsibilities of the Extension Board, receiving rotor-processed ENC data and TTD signals from the last ROT board and routing them to the passive interposer link (toward Stack-Input) and the Cypher Board return path.

Circuit Responsibility	Board Role	Key Component
Mini-Stack Cypher Output	Receives ENC data and TTD from last ROT board; passes return signals (SIG-BLOCK-B/C/F) through stacking connectors toward Cypher Board; routes SIG-BLOCK-A/D/E via passive interposer link to Stack-Input	ERF8 ROT-facing input sockets + SQT-115-01-L-D-RA interposer link

The left edge (front face when viewed from the front of the mini-stack assembly) carries a keyed Samtec QTS-025 male right-angle connector (J1) that mates with the Cypher Board J4 (REF side) or the rear of the previous Rotor Mini-Stack (J2). The right edge (rear face) carries a matching QSS-025 female right-angle connector (J2) for chaining to the next mini-stack (J1) or Stack-Blanking Board. ROT boards connect to J3–J5 (ERF8 female sockets) on the rotor-facing face, receiving signals from the last ROT board in the mini-stack. Return signals are routed to Stack-Input via the passive interposer link at J6 (SQT-115-01-L-D-RA right-angle female on the bottom edge), mating with the Stack-Interposer Board.

Functional Requirements

ID	Functional Requirement	Notes	Satisfied By / Cross-Ref
FR-EXT-03	Pass 3V3_ENIG power and ENC data signals across the mini-stack boundary	Power: received on J1 bottom power section (3V3_ENIG only; no 5V_MAIN); ENC data return: J5 → J6 interposer; ENC passthrough (SIG-BLOCK-B/C): J2 ↔ J1	§5 Power; BOM J1, J2, J5, J6
FR-EXT-05	Connect on the output side to the last ROT board of this mini-stack	J3/J4/J5 = ERF8 female sockets receiving last ROT board ERM8 male output connectors	§6 Interconnects; BOM J3–J5
FR-EXT-07	Protect stacking connector J1 and ROT-facing input connectors J3/J5 from ESD events	J1 and J3/J5 accessible during live mini-stack or rotor swap	§8 Thermal & ESD; BOM U1–U9
FR-SOUT-01	Connect on the front side to the Cypher Board REF side or the rear of the previous Rotor Mini-Stack	J1 = QTS-025-01-L-D-RA-P male right-angle (front / left edge)	§6 Interconnects; BOM J1
FR-SOUT-02	Connect on the rear side to the next Rotor Mini-Stack or Stack-Blanking Board	J2 = QSS-025-01-L-D-RA-K female right-angle (rear / right edge)	§6 Interconnects; BOM J2
FR-SOUT-03	Receive JTAG TTD, TCK, TMS, CPLD_RESET_N and ENC data from the last ROT board of this mini-stack	J3 = ERF8-005 (JTAG); J4 = ERF8-005 (Power — all pins NC); J5 = ERF8-010 (ENC data)	§6 Interconnects; BOM J3–J5
FR-SOUT-04	Route SIG-BLOCK-A ENC data, SIG-BLOCK-E TTD, and SIG-BLOCK-G/H ACTUATE_REQUEST (per DEC-093) from the last ROT board to Stack-Input via the passive interposer link	J6 = SQT-115-01-L-D-RA right-angle female; mates with Stack-Interposer Board TMMH-115-01-L-D-ES male	§6 Interconnects; BOM J6
FR-SOUT-05	Receive SIG-BLOCK-D ENC data from Stack-Input via the passive interposer link and route it into the ROT chain return pass	J6 → J5; ROT chain traversal (left-to-right return direction)	§3 Signal Return Path; §6 Interconnects
FR-SOUT-06	Pass SIG-BLOCK-B ENC return and SIG-BLOCK-F TTD_RETURN toward the Cypher Board via front stacking connector J1	Signals sourced on J2 rear stacking (from blanking board / next Stack-Output passthrough); J2 → J1 internal passthrough per mini-stack	§3 Signal Return Path; §6 Interconnects
FR-SOUT-07	Pass SIG-BLOCK-C ENC reflector signals rearward toward the Stack-Blanking Board via rear stacking connector J2	Signals sourced on J1 (from Cypher Board REF output); J1 → J2 internal passthrough	§3 Signal Return Path; §6 Interconnects
FR-SOUT-08	Terminate JTAG spoke signals at the end of the ROT-chain distribution	TCK, TMS, and CPLD_RESET_N terminate at Stack-Output; R1–R3 idle-state bias resistors (10 kΩ) mirror Cypher Board R3/R5/R6 pattern at spoke end; signals are not returned toward Cypher via the stacking connectors	§4 JTAG Termination; BOM R1–R3

Design Requirements

ID	Design Requirement	Specification	Satisfied By / Cross-Ref
DR-EXT-01	PCB stackup	4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1	§7 PCB Fabrication & Stackup
DR-EXT-07	System quantity	1 per Rotor Mini-Stack; up to 6 per system (30 rotor positions total)	§1 Overview
DR-EXT-12	ESD protection — stacking connector J1 and ROT-facing connectors J3/J5	U1–U4 (J1 signal region: 14 active signal lines + ACTUATE_REQUEST_REF_IN_N/OUT_N via U4's spare channels); U5–U8 (J3 JTAG + J5 ENC data); U9 (J5 ACTUATE_REQUEST_OUT_N/IN_N); within 3mm of connector mating edge per DEC-048/DEC-095	§8 Thermal & ESD; BOM U1–U9
DR-EXT-13	3V3_ENIG entry decoupling bank	C1–C5 (5x 10µF X7R 50V 1206) at 3V3_ENIG entry (J1 bottom power section) per GRS §3 star/spoke pattern	§5 Power; BOM C1–C5
DR-EXT-14	Mounting holes	MH1–MH4: M3 PTH (3.2mm drill) tied to GND_CHASSIS per GRS §4; placement per GRS §4.3 Pattern B. No BOM entry.	§7 PCB Fabrication; GRS §4.3
DR-SOUT-01	Front stacking connector (output/chain side)	J1 = QTS-025-01-L-D-RA-P (Samtec 50-contact right-angle male SMT); fully 50-pin allocated per DEC-092/DEC-093 (this board is the Definition Owner, DEC-094) — ENC data return + TTD_RETURN (SIG-BLOCK-B/C/F), 3V3_ENIG ×8, ACTUATE_REQUEST_REF_IN_N/OUT_N	§6 Interconnects; BOM J1
DR-SOUT-02	Rear stacking connector (chain side)	J2 = QSS-025-01-L-D-RA-K (Samtec 50-contact right-angle female SMT); mirrors J1 signal set with I/O directions inverted (passthrough chain); fully 50-pin allocated per DEC-092/DEC-093	§6 Interconnects; BOM J2
DR-SOUT-03	ROT-facing input connectors	J3 = ERF8-005 (JTAG from last ROT), J4 = ERF8-005 (Power — all pins NC), J5 = ERF8-010 (ENC data from last ROT); mate with last ROT board ERM8 male output connectors	§6 Interconnects; BOM J3–J5
DR-SOUT-04	J4 power pins — 0Ω prototype links	J4 3V3_ENIG pins connected to local 3V3_ENIG plane via R4 (0Ω link); J4 GND pins connected to local GND plane via R5 (0Ω link); both links can be removed to revert to NC if prototype testing reveals EMI issues; see DEC-085	§5 Power; BOM R4, R5
DR-SOUT-05	JTAG spoke termination	R1 = 10 kΩ TCK pull-down to GND; R2 = 10 kΩ TMS pull-up to 3V3_ENIG; R3 = 10 kΩ CPLD_RESET_N pull-up to 3V3_ENIG; placed within 3mm of J3; mirrors Cypher Board R3/R5/R6 idle-bias pattern; per DEC-016	§4 JTAG Termination; BOM R1–R3
DR-SOUT-06	Passive interposer link connector	J6 = SQT-115-01-L-D-RA (Samtec 30-position 2×15 right-angle female shrouded SMT, bottom edge); mates with TMMH-115-01-L-D-ES straight/vertical male on Stack-Interposer Board J1; pin map defined in Stack-Interposer/Board_Layout.md §3	§6 Interconnects; BOM J6
DR-SOUT-07	Power rail	3V3_ENIG only; no 5V_MAIN on this board; no AM circuits requiring 5V_MAIN	§5 Power

Component Block Diagram

flowchart TD
  subgraph stackFront["Stacking Connector — Front (left edge)"]
    J1["J1 QTS-025 male R/A\nENC data return + TTD_RETURN (top 24)\n3V3_ENIG + GND (bottom 10)"]
  end

  subgraph stackRear["Stacking Connector — Rear (right edge)"]
    J2["J2 QSS-025 female R/A\nSIG-BLOCK-B/C/F passthrough\n+ power passthrough\nto/from next mini-stack or blanking board"]
  end

  subgraph rotIface["ROT Board Interface (last ROT output)"]
    J3["J3 ERF8-005 female\nJTAG from last ROT"]
    J4["J4 ERF8-005 female\nPower (all pins NC)"]
    J5["J5 ERF8-010 female\nENC data from last ROT"]
  end

  subgraph interposer["Passive Interposer Link"]
    J6["J6 SQT-115-01-L-D-RA 30-pin female\nSIG-BLOCK-A ENC data + SIG-BLOCK-E TTD\nSIG-BLOCK-D ENC return + SIG-BLOCK-G/H ACTUATE_REQUEST"]
  end

  subgraph esd["ESD Protection"]
    U1U4["U1–U4 TPD4E05 x4\nJ1 stacking connector"]
    U5U8["U5–U8 TPD4E05 x4\nJ3/J5 ROT input"]
    U9["U9 TPD4E05\nJ5 ACTUATE_REQUEST_OUT/IN_N"]
  end

  J2 -- "SIG-BLOCK-B ENC_IN return + SIG-BLOCK-F TTD_RETURN + ACTUATE_REQUEST_REF_IN_N" --> J1
  J1 -- "SIG-BLOCK-C ENC_OUT from Cypher REF + ACTUATE_REQUEST_REF_OUT_N" --> J2
  J1 --> U1U4
  J3 -- "SIG-BLOCK-E TTD + TCK/TMS/CPLD_RESET_N" --> U5U8
  J5 -- "SIG-BLOCK-A ENC data" --> U5U8
  J5 -- "ACTUATE_REQUEST_OUT_N/IN_N" --> U9
  U5U8 -- "SIG-BLOCK-A + SIG-BLOCK-E TTD" --> J6
  J6 -- "SIG-BLOCK-D ENC return" --> J5
  J5 -- "SIG-BLOCK-G ACTUATE_REQUEST fwd" --> J6
  J6 -- "SIG-BLOCK-H ACTUATE_REQUEST return" --> J5
  J1 -- "3V3_ENIG" --> C1C5["C1–C5\n3V3 decoupling"]

Loading

2. Architecture

• PCB: 4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1. ENIG Gold. 2.0mm filleted corners.
• Assembly: Single-sided; no high-density ICs requiring dual-side placement.
• Manufacturer: JLCPCB (standard 4-layer; no special manufacturing constraints).

GND_CHASSIS Single-Point Bond

Per GRS §5: local GND_CHASSIS net tied to mounting holes and enclosure-contact features; no local GND to GND_CHASSIS bond. System's only galvanic bond remains on the Power Module.

3. Signal Return Path

The Stack-Output Board provides passive return routing for the ENC data and JTAG signals within the mini-stack chain. It has no active signal processing ICs; all routing is passive trace continuity.

SIG-BLOCK pass-through signals (J1 ↔ J2)

Signal Block	Signals	Direction	Source on J2 (rear)	Destination on J1 (front)
SIG-BLOCK-B	ENC_IN[5:0] return	J2 → J1	From blanking board or next Stack-Output rear	Toward Cypher REF side
SIG-BLOCK-C	ENC_OUT[5:0] reflector	J1 → J2	From Cypher REF output	Toward blanking board or next Stack-Output front
SIG-BLOCK-F	TTD_RETURN	J2 → J1	From blanking board or next Stack-Output rear	Toward Cypher JTAG Module TDO
—	ACTUATE_REQUEST_REF_IN_N	J2 → J1	From blanking board or next Stack-Output rear	Toward Cypher J4 ACTUATE_REQUEST_REF_IN_N (per DEC-093 step 3, first reflection)
—	ACTUATE_REQUEST_REF_OUT_N	J1 → J2	From Cypher J4 ACTUATE_REQUEST_REF_OUT_N (per DEC-093 step 5, second forward pass)	Toward blanking board or next Stack-Output front

Every Stack-Output board has an internal J2 → J1 passthrough for SIG-BLOCK-B, SIG-BLOCK-F, and ACTUATE_REQUEST_REF_IN_N, and a J1 → J2 passthrough for SIG-BLOCK-C and ACTUATE_REQUEST_REF_OUT_N. These are passive trace routes with no buffering — this board has no active ICs (see §8 Thermal & ESD). Per DEC-095.

Interposer link signals (J3/J5 ↔ J6)

Signal Block	Signals	Direction	Notes
SIG-BLOCK-A	ENC_DATA[5:0]	J5 → J6	Forward-direction traversal result from last ROT board; forwarded to Stack-Input for next-stack or blanking board handoff
SIG-BLOCK-E (TTD)	TTD	J3 → J6	Last ROT TDO — outbound JTAG chain end; forwarded to Stack-Input for next-stack or blanking board handoff
SIG-BLOCK-D	ENC_DATA[5:0]	J6 → J5	Return-direction data post-reflector from Stack-Input; enters ROT chain for return traversal (left-to-right)
SIG-BLOCK-G	ACTUATE_REQUEST (forward)	J5 → J6	Forward pass, collected from last ROT board's own carry mechanism (pin 14, ACTUATE_REQUEST_OUT_N, of Rotor's J6); forwarded to Stack-Input's rear connector via the Stack-Interposer Board
SIG-BLOCK-H	ACTUATE_REQUEST (return)	J6 → J5	Return pass, received from the Stack-Interposer Board (originating at Stack-Input's rear connector); routed into the ROT chain (pin 13, ACTUATE_REQUEST_IN_N, of Rotor's J6) for reverse traversal

Both passthroughs are passive trace routes, consistent with the existing SIG-BLOCK-A/D/E handling on this same connector pair. Per DEC-093/DEC-095.

TTD vs TTD_RETURN naming

Per .copilot/discussions/cypher-system-discussion/extension-mechanical-usage.md Entry 20:

• TTD on the interposer link (J6): the JTAG serial chain signal from the last ROT TDO output, forwarded to Stack-Input. Named TTD here — it is not yet renamed at this point in the chain.
• TTD_RETURN on stacking connectors (J1/J2): the signal renamed at the Stack-Blanking Board after the outbound TTD chain terminates. Propagates from blanking board forward through Stack-Output J2 rear → J1 front on each mini-stack back to the Cypher Board JTAG Module TDO pin.

4. JTAG Termination

TCK, TMS, and CPLD_RESET_N are distributed outbound from Cypher through all ROT boards in the mini-stack and arrive at the Stack-Output J3 ERF8 JTAG connector. Stack-Output is the end of these JTAG spoke distributions — they are not returned toward Cypher.

Idle-state bias resistors R1–R3 are placed at the end of each spoke. They mirror the pull-up and pull-down resistors on the Cypher Board (R3/R5/R6) which hold the same signals in their defined idle states at the source end. Having matching bias at both source and spoke end ensures defined logic levels when a mini-stack is disconnected or powered down during assembly and test. See design/Electronics/JTAG_Module/JTAG_Integrity.md and DEC-016 for system JTAG integrity context.

RefDes	Signal	Termination	Value	Rationale
R1	TCK	Pull-down to GND	10 kΩ	Prevents spurious clocking when spoke stub is floating
R2	TMS	Pull-up to 3V3_ENIG	10 kΩ	Holds JTAG TAP in Test-Logic-Reset state at spoke end
R3	CPLD_RESET_N	Pull-up to 3V3_ENIG	10 kΩ	Holds CPLDs out of reset at spoke end

5. Power

• Power entry: 3V3_ENIG received on J1 (front stacking connector, bottom power section). 3V3_ENIG only — no 5V_MAIN on this board.
• Logic supply: 3V3_ENIG supplies ESD protection ICs U1–U8 and pull-up resistors R2/R3 only. No active logic ICs.
• ROT chain power (J4): J4 3V3_ENIG pins are connected to the local 3V3_ENIG plane via R4 (0Ω link); J4 GND pins are connected to the local GND plane via R5 (0Ω link). This provides parallel power and return-current paths within the mini-stack, reducing effective rail impedance and shortening ROT CPLD switching return paths. Both links can be removed to revert to NC if prototype testing reveals EMI issues. See DEC-085.
• 3V3_ENIG decoupling bank: C1–C5 (5x 10µF X7R 50V 1206) at J1 3V3_ENIG entry; star/spoke topology per GRS §3.
• Power passthrough: 3V3_ENIG passes through J1 (front, bottom power section) to J2 (rear, bottom power section) for the next mini-stack or Stack-Blanking Board.

6. Interconnects

J1 — Front Stacking Connector (QTS-025-01-L-D-RA-P)

Connector definition owner: this board's own Board_Layout.md §1 (IC-REF-CHAIN, per DEC-094). Mates with Cypher Board J4 (first mini-stack) or previous mini-stack J2 (subsequent stacks).

• MPN: QTS-025-01-L-D-RA-P (Samtec 50-contact 0.635mm right-angle male SMT)
• Fully 50-pin allocated per DEC-092/DEC-093 — see Board_Layout.md §1 for the full canonical pin map: ENC_IN[5:0] return (SIG-BLOCK-B out), ENC_OUT[5:0] (SIG-BLOCK-C in), TTD_RETURN (SIG-BLOCK-F out, pin 30), 3V3_ENIG ×8, ACTUATE_REQUEST_REF_IN_N/ ACTUATE_REQUEST_REF_OUT_N (pins 16/35 — passive J1↔J2 passthrough, see §3 Signal Return Path and DEC-095), GND fill.

Pinout: see Board_Layout.md §1.

J2 — Rear Stacking Connector (QSS-025-01-L-D-RA-K)

Connector definition owner: this board's own Board_Layout.md §1 (IC-REF-CHAIN, §1 above — same template, I/O inverted, per DEC-094). Mates with next mini-stack J1 (front stacking male) or Stack-Blanking Board male connector.

• MPN: QSS-025-01-L-D-RA-K (Samtec 50-contact 0.635mm right-angle female SMT)
• Fully 50-pin allocated per DEC-092/DEC-093 — same canonical pin map as J1, I/O inverted; see Board_Layout.md §2.

Pinout: see Board_Layout.md §2.

J3 / J4 / J5 — ROT Board Input Connectors

Mates with last ROT board in the mini-stack (ROT board ERM8 male output connectors on Board A side).

Connector Definition Owner: Rotor/Design_Spec.md §3.4.

Ref	Type	Signal Group	MPN
J3	ERF8-005 (10-pin, female)	JTAG from last ROT (TTD, TCK, TMS, CPLD_RESET_N + GND)	ERF8-005-05.0-S-DV-K-TR
J4	ERF8-005 (10-pin, female)	Power from last ROT — 3V3_ENIG ×5 + GND ×5; connected via R4/R5 0Ω links (see DEC-085)	ERF8-005-05.0-S-DV-K-TR
J5	ERF8-010 (20-pin, female)	ENC data from last ROT, plus ACTUATE_REQUEST_OUT_N/IN_N (pins 13/14, per DEC-093); ESD via U9 (DEC-095)	ERF8-010-05.0-S-DV-K-TR

J4 3V3_ENIG pins connect to the local 3V3_ENIG plane via R4 (0Ω link); J4 GND pins connect to the local GND plane via R5 (0Ω link). Both links can be removed to revert to NC if prototype testing reveals EMI issues (see DEC-085).

J6 — Passive Interposer Link (SQT-115-01-L-D-RA)

Connector Definition Owner: Stack-Interposer/Board_Layout.md.

Right-angle female shrouded 30-position (2×15) connector on the bottom edge. Connects to the Stack-Interposer Board which bridges this connector to the matching return connector on the Stack-Input Board.

• MPN: SQT-115-01-L-D-RA (Samtec 30-position right-angle female shrouded SMT)
• Signals carried (bidirectional):
  • Out to Stack-Input: SIG-BLOCK-A ENC_DATA[5:0] (from J5) + SIG-BLOCK-E TTD (from J3)
  • In from Stack-Input: SIG-BLOCK-D ENC_DATA[5:0] (return direction into ROT chain)
• Mating connector on Interposer Board: TMMH-115-01-L-D-ES (Samtec 30-position straight/vertical male)
• Pinout: see Stack-Interposer/Board_Layout.md §3.

7. PCB Fabrication & Stackup

• Stackup: 4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1.
• Manufacturer: JLCPCB. Single-sided assembly.
• Fillets: 2.0mm rounded PCB corners.
• Mounting Holes: MH1–MH4, M3 PTH (3.2mm drill), tied to GND_CHASSIS per GRS §4. No BOM entry.
• Decoupling: per design/Standards/Global_Routing_Spec.md §3.
• JTAG trace width: All JTAG traces on L1 shall be routed at the CI width per design/Standards/Global_Routing_Spec.md §2.3.1, targeting 50 Ohm controlled impedance. See design/Electronics/JTAG_Module/JTAG_Integrity.md and DEC-016.

8. Thermal & ESD

• Thermal: No active ICs on this board. No thermal concerns.
• ESD — J1 stacking connector (TVS required): J1 is accessible during live mini-stack insertion/removal. Per DEC-045 and DEC-048:
  • U1: 1x TPD4E05U06QDQARQ1 — channels: TTD_RETURN ×2 + ENC_OUT[0:1] (SIG-BLOCK-C)
  • U2: 1x TPD4E05U06QDQARQ1 — channels: ENC_OUT[2:5] (SIG-BLOCK-C)
  • U3: 1x TPD4E05U06QDQARQ1 — channels: ENC_IN[0:3] return (SIG-BLOCK-B)
  • U4: 1x TPD4E05U06QDQARQ1 — channels: ENC_IN[4:5] return, ACTUATE_REQUEST_REF_IN_N, ACTUATE_REQUEST_REF_OUT_N. Per DEC-095. All U1–U4 placed within 3mm of J1 mating edge on L1.
• ESD — J3/J5 ROT input connectors (TVS required): J3 (JTAG) and J5 (ENC) are accessible during live ROT board swap. Per DEC-045 and DEC-048:
  • U5: 1x TPD4E05U06QDQARQ1 — channels: TTD, TCK, TMS, CPLD_RESET_N (J3 JTAG group)
  • U6: 1x TPD4E05U06QDQARQ1 — channels: ENC_IN[0:3] (J5 ENC group)
  • U7: 1x TPD4E05U06QDQARQ1 — channels: ENC_IN[4:5] + ENC_OUT[0:1] (J5 ENC group)
  • U8: 1x TPD4E05U06QDQARQ1 — channels: ENC_OUT[2:5] (J5 ENC group)
  • U9: 1x TPD4E05U06QDQARQ1 — channels: ACTUATE_REQUEST_OUT_N, ACTUATE_REQUEST_IN_N (J5 group, mating with Rotor J6's pins 13/14; 2 channels used, 2 spare). Per DEC-095. All U5–U9 placed within 3mm of their respective connector mating edge on L1.
• Working voltage note: TPD4E05U06QDQARQ1 max continuous working voltage = 5.5V. On 3V3_ENIG (max 3.465V), all U1–U9 within rated limits with >= 2.0V margin.
• ESD — all other connectors (no TVS required): J2 (rear stacking — chain side, not live-swap); J4 (power only, all pins NC); J6 (interposer, internal rigid assembly). Per design/Standards/Global_Routing_Spec.md §9.

9. Branding & Traceability

• Data Plate: Per GRS §6 on Layer L4. Revision block: STAPELAUSGANG [Stack-Output] V1.0.
• Connector Pin-1 Markers: J1–J6 silkscreen pin-1 markers required per GRS §7.1.
• ERF8 labelling: 0.8mm pitch is physically incompatible with 2.54mm connectors; label distinctly on silkscreen.

10. Bill of Materials

RefDes	Specification	MPN	Manufacturer	DigiKey PN	Mouser PN	JLCPCB PN	Alt Supplier + PN	Notes	Footprint Available	Footprint Downloaded	Qty
C1–C5	10µF X7R 50V 1206	CL31B106KBK6PJE	Samsung	1276-CL31B106KBK6PJECT-ND	187-CL31B106KBK6PJE	C43935922	–	3V3_ENIG entry decoupling bank at J1	✔	✔	5
J1	50-contact 0.635mm right-angle male SMT	QTS-025-01-L-D-RA-P	Samtec	QTS-025-01-L-D-RA-P-ND	200-QTS02501LDRAP	C7267889	–	Front stacking connector (mates with Cypher J4 or prev mini-stack J2)	✔	✔	1
J2	50-contact 0.635mm right-angle female SMT	QSS-025-01-L-D-RA-K	Samtec	QSS-025-01-L-D-RA-K-ND	200-QSS02501LDRAK	C6156774	–	Rear stacking connector (mates with next mini-stack J1 or blanking board)	✔	✔	1
J3, J4	10-pin 2x5 0.8mm female SMT	ERF8-005-05.0-S-DV-K-TR	Samtec	SAM13517CT-ND	200-ERF8005050SDVKTR	C7273978	–	J3: JTAG from last ROT; J4: Power (all pins NC)	✔	✔	2
J5	20-pin 2x10 0.8mm female SMT	ERF8-010-05.0-S-DV-K-TR	Samtec	SAM8618CT-ND	200-ERF8010050SDVKTR	C3646170	–	ENC data from last ROT board	✔	✔	1
J6	30-position 2×15 right-angle female shrouded SMT	SQT-115-01-L-D-RA	Samtec	SAM1246-15-ND	200-SQT11501LDRA	C7318577	–	Passive interposer link — mates with Stack-Interposer J1 (TMMH-115-01-L-D-ES); per Stack-Interposer/Board_Layout.md §3	✔	✔	1
R1	10kΩ 1% 0402	ERJ-2RKF1002X	Panasonic	P10.0KLCT-ND	667-ERJ-2RKF1002X	C191123	–	TCK pull-down to GND — JTAG spoke end termination; prevents spurious clocking	✔	✔	1
R2, R3	10kΩ 1% 0402	ERJ-2RKF1002X	Panasonic	P10.0KLCT-ND	667-ERJ-2RKF1002X	C191123	–	R2: TMS pull-up to 3V3_ENIG; R3: CPLD_RESET_N pull-up to 3V3_ENIG — JTAG spoke end termination; mirrors Cypher R3/R6	✔	✔	2
R4	0Ω 0402	ERJ-2GE0R00X	Panasonic	P0.0JCT-ND	667-ERJ-2GE0R00X	C242160	–	J4 3V3_ENIG bus → local 3V3_ENIG plane (0Ω link; remove to revert J4 3V3_ENIG to NC — see DEC-085)	–	✘	1
R5	0Ω 0402	ERJ-2GE0R00X	Panasonic	P0.0JCT-ND	667-ERJ-2GE0R00X	C242160	–	J4 GND bus → local GND plane (0Ω link; remove to revert J4 GND to NC — see DEC-085)	–	✘	1
U1–U8	4-ch bidirectional ESD array USON-10	TPD4E05U06QDQARQ1	Texas Instruments	296-40696-1-ND	595-PD4E05U06QDQARQ1	C81353	–	ESD protection: U1–U4 on J1 signal region, U5–U8 on J3/J5 ROT-facing connectors	✔	✔	8
U9	4-ch bidirectional ESD array USON-10	TPD4E05U06QDQARQ1	Texas Instruments	296-40696-1-ND	595-PD4E05U06QDQARQ1	C81353	–	J5 ROT-facing ESD protection: ACTUATE_REQUEST_OUT_N/IN_N (2 channels used, 2 spare). Per DEC-095.	✔	✔	1