CMD HD Series


    The CMD HD has a 27256 EPROM called the “BOOT ROM”. The latest known version of the BOOT ROM is 2.80. Earlier versions should be upgraded to 2.80 to ensure the drive has all the bug fixes.

    Hold down SWAP 8 and SWAP 9, momentarily press RESET, then release all buttons. This puts the drive into configuration mode where only the BOOT ROM is active and the drive responds to device number 30.

    Show the BOOT ROM version with JiffyDOS:

    73,CMD HD BOOTROM V2.80,00,00

    Show the BOOT ROM version without JiffyDOS:

    0 OPEN 15,30,15 : INPUT#15,A,B$,C,D : CLOSE 15 : PRINT B$

    The first read of the command channel will show the BOOT ROM version. Successive reads will show 00, OK,00,00. To read the BOOT ROM version again, reset the unit into configuration mode again as described above. To exit configuration mode, press RESET.

    Some older BOOT ROM versions do not report the version number on the command channel. I have a BOOT ROM that reports only 73,CMD HD BOOTROM,00,00 but has the string “BOOT ROM VER 2.52” in the ROM.

    The BOOT ROM does not support the RAMLink parallel cable. The HD must be connected via the normal CBM serial port.

    Drive Replacement

    The SCSI drive may be replaced with a newer one but it must be prepared. The HD UTILITIES disk is required. The latest known version of this disk is 1.92. Install the new mechanism with termination and configured as SCSI device 0, then follow this procedure.

    1. Check that your BOOT ROM version is 2.80 and that your HD UTILITIES disk has HD-TOOLS 1.12 and HD-DOS 1.92.

    2. If you have a RAMLink parallel cable, unplug it. You can also disable it with the JiffyDOS command @P0.

    3. You must have no devices on your serial bus configured as device 12 or device 30. The BOOT ROM uses device 30 temporarily and the CMD HD will become device 12 by default when the system is created. You can use HD TOOLS to change the default device number at the end.

    4. If you have a C128, put it into C64 mode.

    5. Start the HD in configuration mode. Turn the power on, then hold down SWAP 8 and SWAP 9, momentarily press RESET, and then release all buttons. You must do this or the HD will lock up the serial bus.

    6. Load and run “LLFORMAT” (low level format). LLFORMAT should recognize your drive. Format it and the program will exit. Formatting may take several minutes and gives no progress indication. Do not reset the HD or the computer when the program exits.

    7. Load and run “CREATE SYS” (create system). This will write the DOS and the system partition. After it has completed, reset the drive and computer.

    8. Load and run “HD TOOLS.64”. This will allow you to set up your partitions and change the default device number. The drive is now ready to use.

    Drive Mounting

    Units where the drive has been replaced by a previous owner may have incorrect or missing hardware. Use the following hardware for a secure mount of a 3.5″ drive:

    – 2x 6-32 1/4″, pan head phillips screw
    – 2x 6-32 3/4″, pan head phillips screw
    – 2x 6-32 5/8″ standoff

    Position the two standoffs over the RTC battery (if equipped) so that the battery can be inspected easily without removing the drive mechanism.

    The SCSI cable should be about 7.5″ long and run cleanly beneath the drive with no folds. If the SCSI cable has been replaced, it may be too long. Excess cabling folded under the drive blocks airflow and should be corrected.

    RTC Battery

    CMD HD units equipped with the real time clock option have a battery soldered to the board. Many of these original batteries are over 20 years old now. They should be replaced or at least inspected for leakage. The original battery in both my CMD HD units was a Tadiran TL-2150/P. It is a 3.6V, 1.0 Ah battery in “1/2 AA” form factor. The “/P” in the part number indicates the leads come soldered on from the manufacturer.

    I have added battery holders to my CMD HD units so the battery can be replaced without soldering. The Tadiran TL-2150/S is the same battery as the original but designed for use in a holder. The holder I used is a Blossom BH-1/2AA PC2. The lead spacing is perfect but the board was not originally designed for a holder and there is not quite enough clearance around it. Spacing the holder off the board with two pieces of double-sided foam tape works around this and is still a secure mount.

    Battery Holder Mod Photos
    Tadiran TL-2150 Datasheet (PDF)

    Parallel Cable

    The CMD HD has a large, 14-pin DIN connector on the back. This is a parallel interface that connects the HD to a CMD RAMLink for faster transfers. This cable may be difficult to find. The Atari ST computers use the same cable to connect an external floppy drive, so searching for an Atari ST drive cable may be easier.

    The RAMLink will detect the parallel cable and use it automatically. Note that HD TOOLS will lock up if the parallel cable is installed and active. Unplug it or disable it with the JiffyDOS command @P0 before running HD TOOLS. The parallel cable can be enabled again with @P1 after exiting HD TOOLS.

    It is also possible to connect multiple CMD HD units to the RAMLink’s parallel port by building a custom cable. All 14 pins are connected 1:1. To my knowledge, the possibility of multiple units was never mentioned by CMD.

    Power Supply

    I have two original power supplies from CMD. One of them came with the CMD HD that I bought directly from CMD in the 90’s, the other came with another CMD HD that I bought secondhand. Both supplies are identical. The outside of the supply identifies it as an Autec “UPS 30-V20P” and the board inside is an Autec “UPS40-2002”. The supply has universal AC input and provides 5VDC @ 2.0A and 12VDC @ 1.5A.

    The output connector of the supply uses the same 4-pin DIN configuration as the 1541-II and 1581, with a small difference. The Commodore supplies have one GND and one NC (no connect) pin but the CMD HD supply has GND on both pins.

    Here are the original electrolytic caps in the supply:

    – C105: 100uF 400V
    – C107: 100uF 25V
    – C117, C118: 1000uF 35V
    – C120, C121: 2200uF 10V

    I replaced the original capacitors with new Nichicon parts with higher ratings than the originals for longer life. I selected these capacitors that are rated for 105°C maximum temperature and 10,000 hour load life:

    – C105: 100uF 400V, Nichicon UCY2G101MHD6
    – C107: 100uF 25V, Nichicon UPX1E101MPD
    – C117, C118: 1000uF 35V, Nichicon UHE1V102MHD
    – C120, C121: 220uF 16V, Nichicon UHE1C222MHD

    Repair Photos
    Autec Adapter Series (PDF)
    Autec UPS40-2002 Datasheet (PDF)

    The CMD HD supply can be used to power a 1541-II or 1581, but I do not recommend using any Commodore supply to power a CMD HD. Most 1541-II and 1581 supplies provide 5VDC @ 1.0A and 12VDC @ 0.5A. There is also a Commodore supply that provides even less: 5VDC @ 0.7A and 12VDC @ 0.5A. The exact power requirement of the CMD HD depends on the hard drive mechanism installed, but both of the Commodore supplies are rated for less current than the Autec supply. Another reason not to use a Commodore supply is that they are linear supplies that can cause overvoltage when they fail. The Autec supply that came with the CMD HD is a switched-mode supply that has overvoltage protection on the 5V side. Repair the original Autec supply or use a similar switched-mode supply with equal or greater ratings.


    CMD HD Schematic (Scanned by Mike Brixius)
    HD UTILITIES Disk – includes HD-TOOL 1.12 and HD-DOS 1.92