USB 27C400 EPROM Emulator

top viewUSB programmable 27C400 EPROM Emulator


This module emulates and is pin compatible with the 27C400 4 Mbit (512Kb x8 or 256Kb x16) EPROM. Instead of requiring a UV eraser and EPROM programmer the module is programmed via a USB connection. With a 2MB FLASH chip on board it can switch between four 512KB images or emulate the larger 27C800 & 27C160 EPROMs.

The 27C400 UV EPROMs have compatible pinout with ROMs used in many computers and electronics from the 1990s. The Commodore Amiga 500/A600/A1200 and Acorn A3020/A4000 all used this ROM pinout. The module can be used as a drop in replacement for the ROMs in compatible systems.

It is programmed via USB from a PC/Mac eliminating the need for an EPROM programmer (+adapter PCBs) and a UV eraser. The module can be programmed in system (ISP) which makes it ideal for ROM software development.

27C400 family EPROMs support byte mode access and it is simple to use this ROM switcher in an 8-bit computer with a suitable adapter PCB.

Highly customisable connections cater for almost any system and use case. It can be adapted for use in almost any equipment that has a ROM or EPROM for data or firmware.


27C400 pinout.png

Directly pin compatible with M27C400 and AM27C400 UV EPROMs.

Warning do not insert module in an EPROM programmer! Vid and Vpp voltages will damage the module. Use USB only.


  • 2MB FLASH chip
  • USB in system programmable (ISP)
  • Emulates 27C200 (256KB), 27C400 (512KB), 27C800 (1024KB) & 27C160 (2048KB)
  • Wire free ROM bank switch function (kickswitch)
  • Highly customisable bank switching
  • 5v TTL compatible inputs
  • 5v CMOS data output (no pullups required)
  • Switchable pinout for JEDEC (27C400) or Commodore A500 rev3/rev 5 ROM
  • Fast <70ns access time
  • BYTE pin supported for 8/16 bit mode
  • Can emulate any 8/16 bit mask ROMs and EPROMs with simple adapter PCBs
  • Link multiple modules for 32 bit (e.g. Commodore A1200, Acorn A4000)
  • USB controlled GPIO
  • LED output


Connect to the module via USB with your PC or Mac and terminal software (e.g. smarTTY or RealTerm v2). Configure and program the module in or out of the target machine via the built in menu system.

Options menu allows quick configuration of module through presets or custom setup.

Program, verify, CRC and dump out the contents from the USB terminal. Built in support for byte swapping so no need to manipulate binary image files on the PC.


Kickswitcher/ROM switching

The 2MB FLASH chip on board allows multiple ROM images to be uploaded and selected with ease. For example in an Amiga 500 with 512KB Kickstart images you can program up to 4 different version of Kickstart and select between them with CTRL+Amiga+Amiga. In most system setups no aditional wires or switches are required to perform image switching.

Moudles can be linked to support ROM switching in 32 bit systems which use two ROMs (e.g. Amiga 1200)

In most installations no additional wires are needed to use the "wire free" ROM switching feature. A wire to the RESET line or physical switch can be added if desired for manual switching. Internal ROM switching can be disabled and managed externally from circuitry or switches by directly connecting to the high address lines allowing ultimate flexibility.

Auto switching can be configured to select a particular ROM on power up or remember the last used ROM.

Development use

The module is ideal for firmware/OS/kickstart development in real hardware. The GPIO pins can be controlled via USB allowing a build, hold in reset, program, release reset cycle to be run as part of a makefile/build process automatically.


The modules emulate an EPROM so can be used directly in any equipment that is compatible with a 27C400 EPROM or mask ROM of the same JEDEC pinout. Simple adapters can be used to allow use in 8 bit computers or to match other EPROM pinouts.

Confirmed working in:

  • Commodore Amiga 500, 600, 1200, 2000
  • Acorn A3020/A4000, RiscPC
  • Acorn Master (with adapter)

Where to buy?

The modules are available for sale on eBay or direct through this website.

Contact me for more information

More detail