Retromaster’s Electronics Projects

…related to old computers and other assorted stuff…

New UFE Design Ready

Posted by retromaster on April 19, 2010

As I’ve indicated in my previous post, I’ve been working on a new floppy emulator design, and it’s ready.

The main idea is to implement (hopefully) fool-proof write support by including enough memory to store at least one MFM-decoded floppy image on board. Obviously, your average 40-pin MCU will not be able to access that much external memory, so it was necessary to switch to a more powerful MCU with more pins (in this case, a PIC32). Although static RAM would be simplest to use, they either do not come in the size required or when they do, they are too expensive. So I decided to use SDRAM instead, as there is still a lot of them out there available cheaply in the form of memory modules.

The PIC32 does not have a built-in SDRAM controller, which makes things a little complicated. Luckily, in this project, the external RAM is used like a fast storage area rather than being randomly accessed. So, the plan is to emulate the SDRAM controller in software. It will be accessed quite a bit slower than the usual 100/133Mhz which makes this somewhat easier. In theory, the PIC32 should be able to handle this task, as in comes with a lot of extra computing power, including a built-in DMA controller.

Besides the addition of memory, this new design is a hybrid between the TFE+ design and the older UFE design in terms of features. It features video output for the user interface, just like in the TFE+. The host system’s keyboard will be used to control the emulator, but the keyboard interface is moved to a daughterboard to make the base design host independent. The basic design elements in the original UFE design are in place (PIC32, SDRAM), but SD card is the disk image storage medium instead of a USB flash drive, mainly to reduce complexity of the firmware and simplify PCB layout a bit.

I’ve already started building the PCB for this design and it’s nearing completion. If all goes well, I may soon have another post with the pictures of the actual board.

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