The D Bit FDADAP board is a small adapter which adapts 8" floppy disk drives (Shugart SA800 style bus) to work with the PC 3.5"/5.25" floppy disk cable pinout. It has 34- and 50-pin connectors which can be connected to the PC floppy controller and the 8" disk drive using simple straight-through ribbon cables (not included), and a 3.5" style power connector for the on-board microcontroller. It also includes a second 34-pin connector for use with real DEC RX50 drives; this configuration is not yet supported by current releases of D Bit software (which use a regular PC 1.2 MB drive for accessing RX50 disks), but support is planned for future versions.
Some 8" floppy disk drives require a "TG43" signal, which tells the drive whether its head carriage is currently positioned at a track number greater than 43 (in which case the drive should use reduced write current). This signal is not normally provided by PC FDCs, so the FDADAP board has a microcontroller which monitors the disk bus and keeps track of the signals related to seeks, so that it knows which track each drive is positioned on, and transparently generates the correct TG43 signal for the currently selected drive with no intervention from host software. The on-board CPU also combines the per-drive "motor on" signals from the PC controller into the common signal used in the RX50 and 8" drive busses.
It should be noted that the FDADAP board only touches the floppy control signals, the data signals are passed straight through so this board will not affect the host controller's ability (or lack thereof) to access 8" single density disks, including DEC RX01 disks. Some controllers can (such as those based on the National Semiconductor PC8477B, or the SMC and Goldstar 37C65 chips), and many can't. In some cases however, controllers that can't write single density disks are still able to read them. In any case, DEC RX02 disks can't be accessed by normal PC style floppy controllers, because the low-level format is a strange combination of single and double density, and doesn't look anything like the IBM System/34-derived double density format supported by PC floppy controller chips.
Price: US $40.00 (including worldwide postage), plus sales tax in MA and NY