FTDI Community

Please login or register.

Login with username, password and session length.
Advanced Search  

News:

Welcome to the FTDI Community!

Please read our Welcome Note

Technical Support enquires
please contact the team
@ FTDI Support


New Bridgetek Community is now open

Please note that we have created the Bridgetek Community to discuss all Bridgetek products e.g. EVE, MCU.

Please follow this link and create a new user account to get started.

Bridgetek Community

Author Topic: ft245 (232 or 2232 in 245 mode) interface to 68000 bus?  (Read 178 times)

mc68000

  • Newbie
  • *
  • Posts: 1
    • View Profile
ft245 (232 or 2232 in 245 mode) interface to 68000 bus?
« on: November 03, 2019, 12:45:38 PM »

Anyone have advice, or an example schematic connecting the 8 bit data bus end of an ft245 as an I/O device to a M68000? (or 6502 for that matter.)

I'm particularly interested in what buffering and what handshake signals, signalling DTACK and IRQ, would be needed, and using whatever modes would enable bi-directional buffering transfers rather than just bitbang and at the highest data rate possible.

This would be to allow me to connect a modern USB computer to an older 68k machine and be able transfer data back and forth.

I realize that on the 68k side I'd need some tri-state logic to detect the I/O address and enable the 68k data bus lines, as well as 5v<->3.3 conversion, but I'm less sure about the handshaking logic to the ft245 side. Ideally I'd like to be to write code on the 68k side to MOVEP bytes in a loop, one at a time, in or out and not potentially lose them. That is to use the internal buffer that the ft245 chips do, so on the modern PC side I could use the driver and read the same byte stream sent by the 68k or write a stream of bytes and have it delivered to the 68k side.

Thanks.
Logged

Jaholmes

  • Newbie
  • *
  • Posts: 2
    • View Profile
Re: ft245 (232 or 2232 in 245 mode) interface to 68000 bus?
« Reply #1 on: December 03, 2019, 04:13:26 PM »

Hey there, mc68000 - Fellow retro computer engineering hobbyist here. :)  I don't have any schematics to share, but I have a few comments:  First off, the FT245 is a 5V-capable device.  Supply 5V to VCC and VCCIO.  No level translation needed.  Regardless of interrupts, you'll still want a way to poll the FT245 for status, as sending a block of data with interrupts between every byte would be horrendous, performance-wise.  So, map the TXE# and RXF# using a tri-state buffer at some other memory location.  You may have other peripherals with similar needs, so you can probably find things to do with the remaining bits.  /DTACK is a larger topic, but if you're using all reasonably fast peripherals and memories you might get away with simply tying /DTACK to ground, as many others have done in simplistic designs.

If your memory map and selection of peripherals are complex, however, you might bite the bullet and throw a cheap PLD into the mix.  A little will go a long way.  I recently did a 6502 build and fit all the address decoding into a $1.50 22V10 chip.  They're still available from Digikey, and you earn extra 'retro' bonus points by programming them in the ancient CUPL language. ;)
Logged