- #Virtual floppy disk emulator how to#
- #Virtual floppy disk emulator serial#
- #Virtual floppy disk emulator software#
It’s solely there to serve as a means to mount the metal bracket to the pcboard. The DB9 connector is not actually connected electrically. This is fine, as this line is also a GPIO, but has the disadvantage or (or advantage depending on how you look at it) of automatically being pulled high during the pi’s boot sequence. Running short on GPIO pins, I used the pi’s RXD line to drive this transistor. I used a 2N3904 to provide an open collector output.
#Virtual floppy disk emulator software#
The other feature I wanted was the ability to have a hardware reset, for those times when the PC is so thoroughly locked up that a software CTRL-ALT-DEL is insufficient. This is an SMD device, which is somewhat unfortunate as I try to avoid SMD devices in my retro builds, but fortunately it is a relatively large and easy to solder package. The 74CBTD3861 includes a dropping diode that is suitable for interfacing 3.3V logic. I chose to use a 74CBTD3861 FET bus switch to remedy this, a suggestion made by a helpful member over at vcfed. This would be high enough to damage the pi’s GPIO interface. I measured the logical high output of the IDT7130 at approximately 4.6V. Pi-to-RAM transfers wouldn’t be a problem, but RAM-to-pi transfers would lead to 5V logic levels being sent to a 3.3V raspberry pi. Interfacing the data bus, however, is more difficult. For signals that are output from the pi and input to the ram (address, control lines), this is relatively simple as the pi’s 3.3V GPIO’s high logic level is sufficient to register as a logical high on the IDT7130. The second task is to interface the dual ported RAM onto the raspberry pi’s GPIO. It’s really no different interfacing this dual ported ram than it would be to interface a static RAM. The ISA bus’s data pins, address pins, and control pins (MEMR, MEMW) connect in the obvious way.
![virtual floppy disk emulator virtual floppy disk emulator](https://i.ytimg.com/vi/8IZcP0oP0OU/hqdefault.jpg)
A 74HCT688 together with dip switches and pull down resistors forms the address decoding logic and provides a chip select to the left port of the IDT7130. The first task is to get the dual ported RAM onto the ISA bus.
![virtual floppy disk emulator virtual floppy disk emulator](http://lh6.ggpht.com/_aGOA7XlvHs4/SeFagWd7UwI/AAAAAAAAAEM/DlcF1kp4t1A/800px-Floppy_Disk_Drives_8_5_3_thumb[3].jpg)
Raspberry Pi virtual ISA drive, schematic
#Virtual floppy disk emulator how to#
I set out to figure out how to interface the IDT7130 to both the PC’s ISA bus and the raspberry pi. A typical example is video cards where one user is the computer updating the video RAM where another user is the display adapter sending the contents of the video ram out to the display adapter.Ĭhecking digikey, I found that a 1 kilobyte dual ported ram does exist, and it’s even through-hole. Dual-ported memory has the advantage that two different users can simultaneously use the memory without interfering with one another. I wanted to come up with something that had the potential for high performance, so I thought I would try a dual-ported memory design. Connecting a modern Raspberry Pi to an ancient ISA computer
![virtual floppy disk emulator virtual floppy disk emulator](http://hxc2001.free.fr/floppy_drive_emulator/SchemaHxCFloppyEmuCPLDz.jpg)
However, I wanted something that would emulate a simple disk device, like a floppy drive, something I could even boot off of, so I implemented a virtual floppy served from a raspberry pi.
#Virtual floppy disk emulator serial#
There are several alternatives, from serial port solutions, to network adapters.
![virtual floppy disk emulator virtual floppy disk emulator](https://hackaday.com/wp-content/uploads/2021/10/arduino-floppy-featured.jpg)
While I can certainly use a KVM switch to interact with the retro computer from my Windows desktop, it would be a lot more convenient if I could also have a shared filesystem. I like to do development at my desk using my modern windows PC. I’m tired of carrying compact flash cards and/or floppies back and forth to my XT computer. In this post, I turn a raspberry pi into a virtual storage device for ISA bus computers: