1541 Ultimate

From ReplayResources
Jump to navigationJump to search
1541Ultimate Logo
Technical Info
ROM 2 MB flash
RAM 32.5 MB (first batch 16.5MB)
Hardware features
  • 3 Buttons - Freeze, Reset and 1541U Freeze (menu)
  • SD card slot
  • IEC bus connector
  • Manual PDF: 28 pages from 1541ultimate.net
    PDF: 2 pages scan of suplied documentation sheet
    CRT ID None
    Programming See 1541ultimate.net
    Attention please!
    The cartridge described in this article is under constant active development - for recent news and data please check: 1541ultimate.net

    1541U is one of the ultimate cartridges for the C64 and regular checks at 1541ultimate.net are a strict requirement for any C64 cartridge lover. It started in 2008 as a hobby project by Gideon Zweijtzer, who then founded the company "Gideon's Logic Architectures" in January 2009.

    Since the 1541U emulates a range of freezer cartridges and allows re-flashing them it is a perfect platform for testing ROMs on the real machine. Cartridge emulation is pretty good and should suit most requirements. This emulation also made the 1541u enter the charts here. There are some problems left as with any other hardware but since this baby can be updated and firmware is publicly available we see a bright future for it.

    Following info mostly from the 1541Ultimate Website:


    The following are the features of the FPGA core, for hardware features see below. Not all features may be available in all versions of the firmware and/or hardware!


    This 1541Ultimate-I (-plus) with ethernet found an awesome home. (Click image for more info.)
    1541Ultimate-II Board
    The new 1541U-II board
    • Flexible freezer menu
      • select, mount, create D64 images, browse disk images
      • create new directories, delete files
      • Ultra fast DMA load of single file programs (directly from SD / from a .D64 with automount and from a .T64 file)
    • Configuration screen, with resident settings
    • Full emulation of a real Commodore 1541 diskdrive. (two drives on 1541U-II)
      • Uses .D64 files stored on SD card
      • Supports .G64 files as well (Read only on fw pre 2.x)
      • Configurable ID
      • Configurable ROM (1541/1541C/1541II or custom)
      • RAMBOard memory expansion (16K)
      • Drive Noise emulation that works with eg 1541-Music or Drive Composer
    • Secondary 'IEC-drive' for direct access to FAT filesystem
      • Can be used in stand alone mode to mount disks into the emulated 1541.
    • FAT/FAT32 support, with sub-directories and long filenames
    • Supports SD V1.1 cards as well as SD V2.0 in High Capacity mode (SDHC)
    • USB storage device (stick, card reader, and even HD) (1541U-II only)
    • ISO9660 support with Joliet, for reading .ISO files and access external CD/DVD drives through USB (1541U-II only)
    • Load of last disk on power up
    • 'Stand-alone mode' (1541U-I fw 1.7)
      • keeps the cartridge port free
      • powered through Mini-USB connector
      • controlled through buttons and IEC.
    • Commodore 1750/1764 REU emulation (1541U-plus, 1541U-II)
    • RR-NET compatible ethernet (1541U-plus version only, fw 1.x only)
      • *NO* Ethernet support yet in stand alone mode!
    • Dual SID implementation, optionally 8 voices each (1541U-II only)
    • Built-in SID player; plays SID files on either 'real' SID or emulated SID. (fw 2.4)
    • PCM output ("Ultimate Audio") (1541U-II only, fw 2.5)
      • Up to 7 voices of sampled audio simultaneously accessible through I/O space
      • 8- or 16-bit samples, up to 48 kHz sample rate
    • Built-in copier (fw 2.6)
    • Command Interface, Accessible module through I/O space that allows direct commands to Ultimate-II (fw 2.6)
    • Ultimate-II DOS V1.0, I/O space driven direct file access to SD/USB (command target) (fw 2.6)
    • Kernal replacement function (fw 2.6)
    • Tape emulation, through 6-pin header on the bottom of the board (requires additional tape connector, fw 2.x)
      • Load .TAP files to C64
      • Capture tape data from a datasette and store it as .TAP file and write .TAP files back to tape, using a Commodore tape deck

    Hardware Specifications

    The basic hardware platform went through 3 revisions so far:


    this describes the first version of the hardware, produced from 2008 to end of 2009.

    • Board size: 68 x 100 mm
    • 250k-gate FPGA
    • Full size 6-pin DIN connector (IEC)
    • 512 kB SRAM
    • 2 MB Flash ROM
    • 16 MB SDRAM
    • Full size MMC / SD card compatible (Mini/Micro SD possible with adapter)
    • Stereo audio output
    • 6-pin expansion pin-header for connection to tape port (for C2N emulation), or other future features.


    as above, with the following differences:

    • 32 MB SDRAM (+16MB for REU)
    • CS8900a ethernet interface (optional since second batch)

    Note: only a small number non-plus boards (with just 16MB RAM) was produced, all later boards were -plus boards.


    this describes the current version of the hardware, produced since 2010.

    as above, with the following differences:

    • Board size: 62 x 84 mm (about 30% smaller than the 1541U)
    • Sturdy plastic case, enforced with glass fiber
    • 700k-gate FPGA
    • MicroSD card compatible slot (instead of a full-size SD)
    • USB host port (supports Mass storage class only)
    • real-time-clock function, for correct file time and date
    • ethernet was removed from the hardware


    slightly revised hardware, available since september 2016.

    • Sturdy ABS plastic case
    • Slightly bigger and faster 1M-gate FPGA
    • 5 MB Flash ROM
    • 64 MB DDR2 SDRAM
    • SD card slot was removed
    • Improved Audio codec (24 bit/96 kHz, for sampled sounds and SID emulation)
    • Full size 6-pin DIN connector (IEC)
    • Audio input added (currently not yet used)
    • Speaker built in
    • 100Mbps Ethernet adapter built in (NOT yet CS8900a/RR-Net compatible)
    • Micro USB for external power
    • Three USB host ports
      • Specialty USB 3.0 port with USB 2.0 signals for storage device OR cable to tape adapter board (for C2N emulation), or other future features.
      • revised tape-adapter, connected via a USB port
    • Dual Flash (no more worry that a software bug or upgrade failure leads to a bricked device)

    Known Problems

    Please understand that due to the nature of FPGA based hardware, many problems might get fixed with a firmware update at some point. For this reason we list only "persistant" problems here, like actual hardware bugs or long standing firmware bugs. For details please refer to the 1541 Ultimate website.


    Freezer bug

    There have been long standing issues with the freezer logic, affecting both emulated cartridges and the menu system. Common symptoms are freezer not reacting at all (perhaps connected to DMA loading), or crash when returning from the freezer to the running program.

    see [1] (requires registration)

    Ethernet bug

    This is a hardware problem with the -plus version of the 1541U board. When the CS8900a chip is enabled, the RAM under the i/o area can not be accessed correctly, which makes some operations impossible (such as transferring binaries to that area using codenet) "Ethernet will never work 100% on the 1541U-I for ALL C64's out there. This is bus-timing related and could only be fixed if some of the timing is revised and other concessions are made."

    see [2] (requires registration)


    see 1541U-II Bug List local copy (retrieved 19 Mai 2014)

    Cartridge problems

    • regular 8k-game and Ultimax cartridges do not work
    • when an unsupported CRT file is loaded, the menu program shows a message, and then the fpga core locks up, requiring a power cycle.


    see 1541U-II+ Bug List (requires registration)







    Since some time official builds of the most recent firmware are no more provided for the (old) 1541U board. Please note that all these archive contents were available from 1541ultimate.net and even though chances are slim, newer versions may be available there!


    • 1541U1-25-kcs.zip (4 May 2016) - 2.5 Firmware with fixed KCS support, compiled by rgc
    • 1541-Ultimate-MK1-2.6d.o918r4.zip (7 November 2013) - Obliterator918′s custom 1541 Ultimate Firmware for “mark 1″ units, Version 2.6d.O918.4 Based on Gideon’s SVN revision 131.
    • 1541u1_172b_with_wvl_fixes.zip (12 December 2010) - 1.72b with WVLs config save flash indication and P00 support, patched with the Ultimate-freezercode from 2.0 firmware (demos like Another Beginning and We Are New now works) and added the (Blu)REU-imagesupport. by Tommi Lempinen


    Please note that all these archive contents are available from 1541ultimate.net and newer versions may be available there!



    Please note that all these archive contents are available from 1541ultimate.net and newer versions may be available there!

    USB fixes:
    support for sticks that do not reliably reply to the 'inquiry' command
    Byte alignment issue fixed when writing. This caused corrupted G64s to be written sometimes
    Support for composite devices added
    Added support for USB keyboards, to navigate the Ultimate browser menu
    Incorporated patches from Markus & Henning, including, but not limited to:
    Audio squeal fix, speaker volume addition
    Ultimate DOS V1.1 with added commands
    Added Home Directory support
    Added support for GeoRAM
    IEC fixes
    IEC now operates properly on the bus, when it is alone (disabled 1541 drives)
    IEC filename fixes; saving a file to IEC adds the right extension and also removes the extension when loading directory
    IEC should now work with JiffyDOS (not yet supporting the JiffyDOS protocol)
    UltiCopy is working again!
    Small fix in TCP support (TCP hangup on retransmission)
    Other small fixes
    Save disk twice bug fixed
    Fixed load errors on tape adapter cable with some USB 3.0 cables
    Keyboard "racekeys" fixed
    Reduced Link Up time for the Ethernet port
    Ultimax mode ROMs now allow video data in ROM


    • 3.0c_433._v4.u2p.zip by markusC64 (Support for Business Basic CRT files, Retro Replay CRT files can be used without patching them before)
    • 3.0c_433._v3.u2p.zip by markusC64 (This version enables a second virtual 1541 drive on the 1541 Ultimate II+)
    • 3.0c_433._v2.u2p.zip by markusC64 (Updated Retro replay modules to 3.8q resp. 3.8y)
    • 3.0c_433._v1.u2p.zip by markusC64 (Simons' Basic can be loaded from CRT, Comal 80 can be loaded from CRT, Westermann learning modules can be loaded from CRT, GeoRAM cartridge support)

    Software supporting special features

    Listing software that requires one or another special feature only available on "modern" hardware and/or emulators, such as the 1541U, Chameleon or VICE.

    16MB REU

    Note: 16MB REU is also implemented by the Chameleon and can also be emulated by VICE.

    Ultimate Audio

    "Ultimate Audio" is a custom 7(?) channel PCM output, which is available in 1541U-II Firmwares 2.5+

    Ultimate DOS

    "Ultimate DOS" is a custom command interface for accessing files on the SD card, which is available in 1541U-II Firmwares 2.5+.


    • Wikipedia deleted the page on the 1541 Ultimate (twice actually). Due to "Unambiguous advertising or promotion" the last time. Well - WiPeD 1541 Ultimate tries to recover it.