SDC_Guide
The VCC SDC dll is an attempt to simulate Darren Atkinson's SDC floppy drive emulator. It is not an emulator but is a simulation that mimics some of, but not all of, the features of Darren's emulator. The simulator is reverse engineered from information found in the CoCoSDC UserGuide and other sources as well as from tests of software designed to work with the SDC.
Some SDC features have been left out and the special SDC SDF file format is not-supported. Some implimented features may not work properly, these are usually not intentional but are due to a mis-understanding of how a real SDC works.
Some of the games found on the 'Coco SDC Image.zip' appear to be incompatible with the simulator. Some of these games are likely intended for Coco1 and Coco2, which may explain why they don't run on a Coco3.
The SDC uses Coco's disk ports. Disk ports are in the range $FF40 through $FF5F and are special in that the Multi Pak Interface can direct which slot has access to them by using the Spare Cartridge Select Signal (SCS). SDC-DOS uses this to select either the SDC or the Floppy driver to choose SDC emulated disks or a real floppy when doing disk I/O.
An enhancement to Vcc's mpi.dll was required to selectively control port isolation. It is recommended the FD502.dll be in mpi slot 4 and SDC.dll be in mpi slot 3 with slot 3 selected. If the MPI version you are using has a Disable Cart Select checkbox it should not be checked when using the SDC dll.
The VCC SDC emulator supports JVC, VDK, OS9, and raw images. It does not support SDF images. SDC.dll expects image files to contain a contigous array of 256 or 512 byte sectors preceded by an optional header of less than 256 bytes. If a header is recognized it is examined to determine the number of sides on the virtual disk. If there is no header the number of sides is inferred from the image size. When images are mounted as "raw" no attempt to detect a header is done.
For performance reasons most emulators, including VCC, use a pair of unused disk ports (the Becker interface) to communicate with a drivewire server via a TCPIP socket connection. However, SDC-DOS is designed to work with a CoCo and that uses the bitbanger to connect to a drivewire server. This means it does not interface to the Becker drivewire on Vcc. A custom SDC-DOS could be modified to use the Becker interface. This work is best done by those with experience in such modification.
SDC.dll maintains a list of rom files (banks) that can be loaded using sdc flash control command. The content of a rom file is loaded into sdc's cart rom when selected. The roms can be accessed using the SDC-DOS 'RUN@n' command.
The bank active at startup can be selected from the SDC config menu. Normal SDC operation requires that the startup bank (default zero) contains the SDC-DOS rom. If this bank is left empty SDC.dll will automatically load SDC-DOS.rom from the VCC execution directory.
Using RUN@ to switch to disk11.rom will start the rom but will not set the MPI slot select, a poke is required after DECB starts up to allow floppy operations. The address to poke is 65407 ($FF7F) and the value depends which MPI slot FD502.DLL is in. Poke 0 for slot 1, 17 for slot 2, 34 for slot 2, and 51 for slot 4.
The currently selected MPI slot can be seen on the VCC status line. It is displayed as MPI:x,x where x,x are digits showing slot numbers. The first digit shows which slot contains the ROM being run, the second digit shows which slot gets floppy control signals. The above pokes set both digits to the same slot.
SDC-DOS assumes a self centering joystick is being used. This means that "mouse" is not a good option for joystick emulation. It might be better to use "keyboard" or avoid using joystick mode if you do not have a WASD or self centering controller. Also if VCC is overclocked SDCX will be difficult to control.
It has been discovered that some games can damage the virtual disk SDCEXP.DSK if it is mounted in drive 0. Once SDC Explorer is configured the way you like it is recommended that SDCEXP.DSK be set to read only on the system, or to keep a backup handy.
SDC.dll contains a Cloud9 RTC clock emulation. Software that can access this clock can use it to get the date and time.
The setup I have used to test with is as follows.
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In Cartridge/MPI config place FD502.DLL in slot 4, SDC.DLL in slot 3. Select slot 3 and make sure "Disable Cart Select Signal" check box is NOT checked.
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Download a Coco SDC Image.zip from the Coco Archive. I have been using the 2025-04-30 version. Unzip the contents into a directory of your choice.
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If you intend to use SDC Explorer's "RESTORE LAST SESSION" feature (set by default) in that same directory create an empty SDCX.CFG file to store session information. If "RESTORE LAST SESSION" is checked in the explorer's Config and this file is corrupted the explorer will display an "SDC NOT READY" error and image loading will not work properly.
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In Cartridge Cartridge/SDC config int the SD Card Path box enter or locate the path to the directory created. Leave everything else blank for now. Hard Reset to to start the simulation. (F9 twice or shift F5)
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Type EXP to start the explorer if it does not auto start. If you hold the 'C' key down while it the explorer starts the configure screen comes up. Once the explorer is configured the way you want it is recommended that the SDCEXP.DSK be write protected at the system level (Set the file ReadOnly in Windows) to prevent accidental damage to it.
The SDC Config dialog is reached by selecting Cartridge/SDC Config.
SD Card Path: At the top you can enter the SD card path. This can be any Windows directory that you have write access to or it could be an actual SD card mounted on windows. If you click on the '>' button a dialog comes up that allows you to select the directory.
Flash Banks: This is a list of the rom files that simulate the SDC flash bank. Clicking on '>' brings up a dialog that lets you select the rom. The bank used at VCC startup or hard reset can be set in the Startup Bank box. If SDC.dll is selected in MPI then the startup bank should contain SDC-DOS. If the startup bank is left empty the simulator (SDC.dll) will try to load SDC-DOS.rom from VCC's execution directory. If a bank is not empty an 'X' button is displayed to empty it.
Enable Clock: This check box enables the Cloud9 clock. Replace the clock2 driver with clock2_cloud9 in OS9boot to use it. Alternately you can use the disto Clock in the fd502.dll. The Disto clock is subject to floppy bank isolation but should still work with Nitros9 most of the time.
The "OK" button saves the settings to the Vcc ini file and exits the config dialog.
There is also a SDC Control dialog reached by selecting Cartridge/SDC Control. This dialog is a small window showing the disk currently loaded in SDC drive 0 and a "Next Disk" button. The button selects the next disk found in the current directory. Moounting a diectory (DRIVE #, "directory") automatically loads the first disk in "directory".