Electronics System Architecture - thepinkmile/Enigma-NG GitHub Wiki

Enigma-NG System Architecture

Status: Draft Project: Enigma-NG Author: Izzyonstage & GitHub Copilot Version: v1.0.0 Associated Hardware Revision: Rev A Last Updated: 2026-04-20

1. Board Hierarchy and Physical Structure

The Enigma-NG system comprises the following boards:

  • Controller Board (CM5) โ€” Raspberry Pi CM5 carrier and the mechanical motherboard of the machine. Hosts the external RJ45, Ethernet ESD/magnetics, PoE front-end, HDMI, USB 3.0, and the dock interfaces to both the Power Module and the Stator.
  • Power Module โ€” Removable power-conditioning / UPS cartridge. Accepts local USB-C and battery inputs plus a regulated PoE-derived auxiliary feed from the Controller; generates 5V_MAIN and 3V3_ENIG, manages hold-up energy, and remains the only intentional GND โ†” GND_CHASSIS bond.
  • Stator โ€” Removable vertical daughterboard mounted from the enclosure wall. Receives power and logic from the Controller through two hybrid blind-mate connectors; fans power and JTAG into the rotor stack and hosts the routing / reflector CPLD.
  • Settings Board โ€” Panel-mount switch and RGB indicator board on the shared Stator I2C-1 bus; provides user-facing routing/reflector configuration input.
  • Rotors (ร—30) โ€” Arranged in groups of 5, chaining directly output-to-input. An Extension Board sits between each group of 5 to re-buffer broadcast signals.
  • Extension Board (up to ร—5 within Rev A power budget) โ€” Bridges between rotor groups; re-buffers TCK and TMS. Minimum configuration: Stator โ†’ [5 Rotors] โ†’ Reflector (0 Extensions, 5 rotors). Full build: 6 groups of 5 rotors separated by 5 Extension boards, terminated by the Reflector (30 rotors total).
  • Reflector โ€” Mandatory end-of-chain turnaround board after the final rotor; provides the physical ENC return path and routes TTD_RETURN back to the Stator while the selected reflection map is applied by the Stator CPLD.
  • Encoder Modules (ร—6) โ€” 1 KBD_ENC, 1 LBD_DEC, and 4 plugboard modules (PLG_PASS1_DEC, PLG_PASS1_ENC, PLG_PASS2_DEC, PLG_PASS2_ENC). Connect to the Stator in three banks of two identical 26-pin IDC ports.
  • JTAG Daughterboard โ€” USB Blaster II implementation for programming CPLDs.

Physical Chain

          external RJ45 / HDMI / USB3
                     |
                Controller Board
                 /             \
        J1/J2/J3         J4/J5
               |                |
          Power Module       Stator
                                |
                         J1โ€“J3 Rotor 1
                                ยท
                             Rotor 5
                                |
                          Extension 1
                                |
                             Rotor 6
                                ยท
                             Rotor 30
                                |
                            Reflector
                                |
                    TTD_RETURN -> Stator J10

The Power Module and Stator are both removable daughtercards. The Controller is the fixed mechanical reference that mates to both boards and owns all enclosure-edge I/O.

2. Interconnect Architecture

2.1 Controller โ†” Power Module

The Controller โ†” Power Module dock uses three 10-position TE 2.5 mm board-to-board connectors:

Link Function Controller side Power Module side
J1 Main regulated rails (5V_MAIN, 3V3_ENIG, GND) TE 1-1674231-1 receptacle TE 1123684-7 plug
J2 Regulated PoE-derived auxiliary input (VIN_POE_12V + GND) TE 1-1674231-1 receptacle TE 1123684-7 plug
J3 Low-speed control / telemetry (I2C-1, PM_IO_INT_N, PWR_GD, ROTOR_EN, PWR_BUT) TE 1-1674231-1 receptacle TE 1123684-7 plug

Functional allocation:

  • J1: 3 ร— 5V_MAIN, 2 ร— 3V3_ENIG, 5 ร— GND
  • J2: 3 ร— VIN_POE_12V, 7 ร— GND
  • J3: I2C1_SDA, I2C1_SCL, PM_IO_INT_N, PWR_GD, ROTOR_EN, PWR_BUT, 4 ร— GND

Reference PDFs: TE-1-1674231-1-datasheet.pdf, TE-1123684-7-datasheet.pdf

2.2 Controller โ†” Stator

The Controller โ†” Stator dock uses two Molex EXTreme Guardian HD hybrid connectors:

Link Function Controller side Stator side
J4 5V-biased power dock Molex 2195630015 receptacle Molex 2195620015 plug
J5 3V3/JTAG/I2C dock Molex 2195630015 receptacle Molex 2195620015 plug

Functional allocation:

  • J4 power blades: 4 ร— 5V_MAIN, 1 ร— GND
  • J4 signal field: additional GND returns / guards
  • J5 power blades: 4 ร— 3V3_ENIG, 1 ร— GND
  • J5 signal field: guarded TCK, TMS, TDI, TTD_RETURN, I2C1_SDA, I2C1_SCL, with all remaining signal contacts tied to GND

The small signal contacts are valid current-carrying return paths as well as guards; the family specification rates them at 4.5 A/contact.

Reference PDFs: Molex-2195630015-datasheet.pdf, Molex-2195630015-drawings.pdf, Molex-2195620015-datasheet.pdf, Molex-2195620015-drawings.pdf, Molex-ExtremeGuardianHD-2141130000-PS-000-specification.pdf

2.3 Rotor-Stack Connectors

All rotor-stack interconnects remain on the Samtec Edge-Rate series 0.8 mm board-to-board connectors:

  • ERM8 โ€” male header (originating / input side of a connection)
  • ERF8 โ€” female socket (receiving / output side of a connection)

These connectors are used only for the rotor / extension / reflector chain.

3. Power Architecture

The Power Module produces two rails from three upstream sources:

  • Controller-fed PoE auxiliary: VIN_POE_12V enters the PM from the Controller after the RJ45, PoE PD, transformer, and cable-entry EMI/ESD stages.
  • Local USB-C PD input: handled on the Power Module.
  • Local smart-battery input: handled on the Power Module.

Generated rails:

  • 5V_MAIN โ€” Up to 12A; dual-phase interleaved LMQ61460-Q1
  • 3V3_ENIG โ€” Clean 3.3V; TPS75733KTTRG3 LDO post-regulator

Grounding Rule

The Controller may implement local shield/chassis handling for enclosure-entry connectors such as RJ45, but the only intentional DC bond between GND and GND_CHASSIS remains on the Power Module at the main power-entry boundary before the eFuse. No second bond is permitted on the Controller or Stator.

3V3_ENIG Power Flow

Power Module (TPS75733KTTRG3 LDO)
  -> Controller Board (via J1)
    -> Stator (via J5 power blades)
      -> Rotor group 1
      -> Extension reinjection points
      -> final reflector return harness

4. JTAG Serial Chain (TTD Net)

TTD Net Name

The JTAG serial chain data pin is designated TTD (JTAG Transmission Data) at pin 6 on all rotor-stack JTAG connectors. This unified name avoids TDI/TDO direction confusion:

  • On the input side (J1 pin 6): TTD carries incoming TDI from the previous stage.
  • On the output side (J4 pin 6): TTD carries outgoing TDO to the next stage's TDI.

Serial Chain Path (Controller -> Reflector -> TTD_RETURN)

Controller J5
  -> Stator CPLD
  -> Stator J1 pin 6 (TTD out)
  -> Rotor 1 ... Rotor 30
  -> Reflector J1 pin 6 (TTD in)
  -> Reflector J4 pin 15 (TTD_RETURN)
  -> Stator J10 pin 15
  -> Controller J5

TCK and TMS โ€” Broadcast Signals

TCK and TMS are broadcast signals. They leave the Controller via the Stator J5 logic dock and then propagate through the rotor chain in parallel.

Extension Board Signal Buffering

Every 5 rotors, an Extension board re-buffers TCK and TMS using a 74LVC2G125 dual-buffer IC (U1). TTD is NOT buffered at Extensions โ€” it is a serial chain signal and must pass uninterrupted through each CPLD.

Signal Integrity

Component Location Value Purpose
TTD path Rotor stack board-to-board hops Direct No per-rotor series resistor on the BtB chain
R1 Reflector TTD input 22ฮฉ series Reflector end-of-chain TTD termination
R2 Each Rotor 10kฮฉ pull-up TMS default-high
R3 Each Rotor 10kฮฉ pull-up TDI default-high
R4 Each Rotor 10kฮฉ pull-down TCK default-low
R5 Each Rotor 10kฮฉ pull-up SYS_RESET_N default-high (inactive)

5. I2C Topology

All system management devices remain on the single shared I2C-1 bus:

Address Device Location Function
0x09 LTC3350 Power Module Supercap charger/monitor
0x0B Smart Battery Power Module SMBus battery monitoring
0x28 STUSB4500 Power Module USB-C PD controller
0x3F PCA9534A Power Module PM-local status + SW1 RGB handoff expander
0x40 INA219 Power Module 5V_MAIN telemetry
0x45 INA219 Stator Rotor-stack telemetry
0x20 MCP23017 Stator ENC monitoring
0x21 MCP23017 Stator Virtual keypress + servo control
0x22 MCP23017 Stator CPLD config output driver
0x23 MCP23017 Settings Board Switch input reader
0x24 MCP23017 Settings Board Bank 1 LED controller
0x25 MCP23017 Settings Board Bank 2 LED controller
0x60 PCA9685 Stator Servo PWM driver

The PM-local expander uses the address block adjacent to the PM INA219 so PM devices remain grouped in i2cdetect output.