How feasible is it to use one port of a 6522 (e.g. 8 data lines + CA1/CA2 or CB1/CB2) to create a directional connection to a microcontroller?

I originally intended two use both ports to communicate (one for input, one for output) with hardware handshaking but I'm now wondering if I could get away with only using one port and reconfigure it on the fly.

The microcontroller will be running firmware to access a filing system on either a SD/MMC card, or more likely, some Disc-On-Chip devices. The data passed thru the 6522 will instruct the microcontroller which operation is required followed by the arguments.

_________________
Andrew Jacobs
6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs

Anything is possible. You will have to work out the handshaking so you don't cause contention on the bus. You may need to use a few IO pins from the other port to facilitate the handshaking. More specs would allow for a better answer.

This sounds interesting... care to share more details. Is this something like the the uALFAT?

http://www.ghielectronics.com/products.php

Daryl

Microchip have recently released the C source for a FAT16 driver for 18/24/33F devices (which I have the development tools for) and I acquired a large number of 48MB Disk-On-Chip devices (look up MD2202-D48) from eBay for next to nothing so I thought I'd combine the two things.

I'd have to write the code to drive the interface to the 6522 and the Disk-On-Chip but I don't think thats much code, certainly less than writing a complete filing system in 6502.

_________________
Andrew Jacobs
6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs

Since both the PIC and the 65C22 have bi-directional IO's, you can certainly build a bi-directional bus. Also, since you are in control of the PIC interface, you can design the handshaking for both ends.

That will be a good project. Sounds like it could be a great file system.

Daryl

Do you really need the data to go so fast that a serial interface (even if you had to bit-bang it) won't do? It sure makes construction simpler.

I was thinking of putting together something like this to add into my system. Two Disk-On-Chips with 18F4620 controller and two octal d-type flipflops to latch the address.


My homebrew system is based on 1Mhz Rockwell chips I salvaged a long time ago. Its designed as a set of 160mm by 100mm cards.

The CPU card looks like this. The PLD is used to create a bus signal when the target address is either zero page (used to disable the ROM) or the I/O page.

The memory card supports 64K of RAM and a disableable 4K ROM.

Designed but not yet built is a dual 6522 IO module.


I'm also working on a PIC based USB CDC interface so my system can be connected to a PC and well appear as a COM port that you can connect to with HyperTerminal. Again I was going to communicate with this through one of the VIAs. It may also draw its power from the USB.

_________________
Andrew Jacobs
6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs