Multicard emulator with a drive for computers with ISA bus
You can use a null modem cable or an SD-IDE adapter to communicate with a computer with an ISA bus. And here is another handy device: a multi -card emulator with a disk drive based on the IDT7130 chip — dual-port 1 kilobyte RAM. It interacts, on the one hand, with the ISA bus of your vintage computer, and on the other, with the “raspberry” installed directly on the emulator board.
Two other chips on the board - 74HCT688 and 74CBTD3861. The first of them allows you to select the address of the DIP-switches and generates a signal "chip select". Hi from the pre-PnP era. The second is used as a level converter. The DB-9 connector is not connected anywhere, it keeps the mounting bar on the chassis on the board. Two transistors form the reset and power control signals, the second one is useful if an ATX type PSU is installed in the computer.
The board can work in two modes. The first of them requires pre-loading the resident BIOS extension from some other drive, in which case the drive emulator cannot be bootable. In the second mode, “raspberry” writes the expansion to dual-port RAM, and it takes up half of its capacity, then the “drive” can be a boot drive and even the only drive in the system, but it works at a slightly lower speed.