Hardware Integration (Carrier Board)

Table of contents
  1. Overview
  2. Carrier board requirements
    1. Layers, routing, and signal integrity
    2. Trace width guidance
    3. Power and ground
    4. Optional indicators
  3. Soldering & inspection
  4. Powering
    1. 1) Power from the carrier board (+5V)
    2. 2) Power from USB-C (+5V)
    3. Powering both at the same time

Overview

The ROM Emulator module must be integrated into host hardware. In most real-world builds, that means the ROM Emulator is soldered onto a custom carrier board that adapts it to the target system’s ROM socket/pinout and mechanical constraints.

Carrier board requirements

A ROM Emulator carrier board typically has two functional sections:

  1. Castellated section (ROM Emulator module footprint)
    • This section is used to solder the ROM Emulator PCB onto the carrier.
    • The carrier can provide a solder mask / footprint variants for different ROM Emulator module models.
    • The carrier-side footprint can be implemented as through-hole or SMD, depending on the module and assembly preference.
  2. ROM/EPROM/EEPROM “chip” section (target pinout adapter)
    • This section must mimic the pinout of the device you want to emulate.
    • In practice, this is usually implemented as a through-hole DIP footprint (or equivalent), matching the target socket/package.

Layers, routing, and signal integrity

  • The carrier PCB can be 2-layer or 4-layer.
  • Prefer non-crossing routes for critical address/data/control lines.
  • If signal lines must cross, route them so there is a solid GND and/or +5V region between them (this is a key reason why 4 layers can be a better option).

Trace width guidance

  • Recommended minimum trace width for signal lines: 1.27 mm.
  • For bus speeds below ~16 MHz, thinner traces can still be safe depending on the target system.
  • Typical widths we use: 2.5 mm down to 1.27 mm.

Power and ground

  • The carrier must provide +5V power and a good ground connection to the ROM Emulator.
  • Additional local decoupling capacitors on the carrier are not strictly necessary: we assume the target motherboard already has decoupling in the ROM/EPROM/EEPROM area.

Optional indicators

  • It can be useful to add LEDs to observe line activity on the carrier.
  • However, the ROM Emulator board already provides LEDs for Power, Emulation, and Volume (ROMEMUL), so extra LEDs are optional.

Soldering & inspection

There are two common ways to mount/solder the ROM Emulator module to the carrier board:

  1. Through-hole headers (stacked)
    • Use two interleaved 2.54 mm headers, typically 2× 20 pins.
    • This is a robust and very build-friendly option.
  2. Direct castellated soldering (recommended for tight builds)
    • Solder the ROM Emulator directly via its castellated edges onto the carrier footprint.
    • This is generally the best option when vertical clearance/space is restricted.

Both approaches are perfectly valid; choose based on mechanical constraints and the target enclosure.

Powering

The ROM Emulator can be powered in two ways:

1) Power from the carrier board (+5V)

  • If the ROM Emulator is fed with +5V from the carrier board, the firmware assumes it must start in EMULATION mode.
  • In this mode, the green LED is on and ROM emulation starts immediately, ready to work inside the target motherboard.

2) Power from USB-C (+5V)

  • If the ROM Emulator is fed with +5V via the USB‑C connector, it starts in Volume (ROMEMUL) mode.
  • This is the expected mode when connecting the device to a computer to manage ROM images on the ROMEMUL mass-storage volume.

Powering both at the same time

  • It is safe to feed both power sources at the same time.
  • When USB‑C power is detected, Volume (ROMEMUL) mode prevails.

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