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EPiC - A new 68k multi-processor motherboard project
http://anycpu.org/forum/viewtopic.php?f=23&t=135		 Page 11 of 18
Author:  mercury0x000d [ Wed Jul 30, 2014 4:02 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
Garth wrote:
The 74HC154 is available in 24-lead SOIC, a .300'-wide DIP, and a couple of other packages. http://www.mouser.com/Search/Refine.asp ... rd=74HC154
Same for 74HCT154. http://www.mouser.com/Search/Refine.asp ... d=74HCT154
Unfortunately, no 74AC or 74ACT or 74ABT, at least not at Mouser.

Drawing buses makes it easier to follow idividual lines. They are always labeled where the enter/exit a "bundle" or connect to something.


I'll have to add some buses then! The next revision should be a little cleaner. :)
Author:  mercury0x000d [ Wed Jul 30, 2014 4:04 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
Dr Jefyll wrote:
Doh! -- sorry. The concern I raised about putting the DUART on D15-D8 was unfounded. What you've done is perfectly OK. (On some processors it would mean the DUART data would appear in D15-D8 of the register, and that would be a nuisance coding-wise.)

On the bright side, checking this issue gave me a chance to drag out my decades-old Motorola Microprocessors Data Manual. I'm always glad to have an excuse to go thumbing through that venerable tome. :)


When I thought it through in my head it seemed like it would be okay, but I wasn't sure. I know you guys have a lot more experience at this stuff than I!

By the way... anything in there of particular interest on the '060? :D
Author:  mercury0x000d [ Wed Jul 30, 2014 4:08 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
I know the purpose of VCC/VDD/VEE/VSS (meaning I read the appropriate Wikipedia article lol) but I don't know what significance the difference is to Eagle. For example, I want DTACK grounded in the dev board, so I connected it to the ground symbol only to have Eagle complain. I tried connecting it to a common pin along with other things which need grounded. More complaints. Only when I tied DTACK to VSS did I hear no protesting from the software. Does it matter? Can't I just tie everything to GND and override the errors and warnings? Or is there some significance I'm missing here?
Author:  barrym95838 [ Wed Jul 30, 2014 5:03 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
mercury0x000d wrote:
... I want DTACK grounded in the dev board ...

Sorry for drifting a bit here, but have you checked out this eccentric news letter?

http://www.easy68k.com/paulrsm/dg/

I read somewhere that Hal is no longer with us, but his voice still comes through loud and clear in these great articles, at least for me.

Mike
Author:  mercury0x000d [ Wed Jul 30, 2014 5:48 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
barrym95838 wrote:
mercury0x000d wrote:
... I want DTACK grounded in the dev board ...

Sorry for drifting a bit here, but have you checked out this eccentric news letter?

http://www.easy68k.com/paulrsm/dg/

I read somewhere that Hal is no longer with us, but his voice still comes through loud and clear in these great articles, at least for me.

Mike


No need for an apology! I have read through those, and indeed they're full of the author's unique perspective on things.

I think he and I would have gotten along well. :)
Author:  mercury0x000d [ Tue Aug 05, 2014 4:02 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
Just to show I haven't been being lazy...

:lol:

Attachments:
EPiC dev board revision 2.gif
EPiC dev board revision 2.gif [ 165.09 KiB | Viewed 7355 times ]
Author:  mercury0x000d [ Sun Aug 17, 2014 1:23 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
I'm a bit confused on how I should tie the PS/2 ports into the DUART. Has anyone done this before? Soon as this part gets wrapped up, I'm just about ready to start designing the board.
Author:  BigEd [ Sun Aug 17, 2014 9:39 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
I think there's some subtlety needed for PS/2. Some references
http://www.computer-engineering.org/ps2protocol/
http://www.pyroelectro.com/tutorials/ps ... heory.html

Note that there's a clock, so a UART might not be what you need. Looks like most solutions use bit-banging - either using the main processor or a subsidiary embedded processor like an AVR.
http://codeandlife.com/2013/06/28/minim ... ttiny2313/

Cheers
Ed
Author:  mercury0x000d [ Mon Aug 18, 2014 1:58 pm ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
BigEd wrote:
I think there's some subtlety needed for PS/2. Some references
http://www.computer-engineering.org/ps2protocol/
http://www.pyroelectro.com/tutorials/ps ... heory.html

Note that there's a clock, so a UART might not be what you need. Looks like most solutions use bit-banging - either using the main processor or a subsidiary embedded processor like an AVR.
http://codeandlife.com/2013/06/28/minim ... ttiny2313/

Cheers
Ed


Okay, that makes sense. I wasn't sure if it could be interfaced directly to the DUART or no. Do you think it could be bit-banged using the auxiliary I/O pins of the DUART?

Speaking of which, is there a chip in existence which takes, say, an address in and provides an array of bit outputs? Kinda like an addressable shift register.
Author:  BigEd [ Mon Aug 18, 2014 2:07 pm ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
If you have a couple of pins and you think you can meet timing, you should be fine.
See
http://sbc.rictor.org/io/pckb6522.html (via http://forum.6502.org/viewtopic.php?p=10924#p10924)
or for a fallback
http://www.adafruit.com/products/1136

Edit: for your other question, perhaps you want a demux? http://margo.student.utwente.nl/stefan/ ... /demux.htm
Author:  mercury0x000d [ Mon Aug 18, 2014 3:09 pm ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
Actually, I don't think the DUART I/O pins will work because the PS/2 communication is bidirectional and the DUART has separate input and output pins. The Adafruit module is nice, but I'd prefer not to rely on third-party assembled parts although it sure would make things simpler. Ugh, decisions...

What do you think about using a BASIC Stamp as an assistant I/O processor?
Author:  stefanberndtsson [ Mon Aug 18, 2014 3:14 pm ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
mercury0x000d wrote:
Actually, I don't think the DUART I/O pins will work because the PS/2 communication is bidirectional and the DUART has separate input and output pins. The Adafruit module is nice, but I'd prefer not to rely on third-party assembled parts although it sure would make things simpler. Ugh, decisions...

What do you think about using a BASIC Stamp as an assistant I/O processor?


I'd go for an AVR or a PIC, or even an Arduino (for example a pro mini). My guess is that you'll get far better timing control with one of those compared to a BASIC Stamp.
Author:  Garth [ Mon Aug 18, 2014 7:05 pm ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
mercury0x000d wrote:
Actually, I don't think the DUART I/O pins will work because the PS/2 communication is bidirectional and the DUART has separate input and output pins.

According to a quick look at the DUART data sheet at http://www.jameco.com/Jameco/Products/P ... 464958.pdf, its general-purpose outputs can be configured as open-drain; so then you would pair it with an input, ie, have both an input pin and an output pin on the same line. The open-drain output can pull the line down at any time, but the input can read the line at any time too.

Quote:
What do you think about using a BASIC Stamp as an assistant I/O processor?

Echoing Ed's comment, microcontrollers can support functions like that where you don't need tight control of the timing, but I think the BASIC Stamp will be much too slow. You'll probably want one of the uC's he mentions, programmed in assembly or at least compiled from a higher-level language that gets turned into assembly.
Author:  mercury0x000d [ Tue Aug 19, 2014 1:36 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
Thanks, guys. Great info as always :)

What you pointed out on the 68681 never occurred to me! That would make for a quite easy to implement this function, but I think to save processing time and gain experience I'll just start experimenting with AVRs now. I know I'll need one for the 68060 board anyway, so why not? I found something called Great Cow BASIC which compiles QBASIC-like syntax down into AVR assembly, which will fit in nicely with the project's newbie-friendliness :)
Author:  Dr Jefyll [ Wed Aug 20, 2014 2:35 am ]
Post subject:  Re: EPiC - A new 68k multi-processor motherboard project
mercury0x000d wrote:
Speaking of which, is there a chip in existence which takes, say, an address in and provides an array of bit outputs? Kinda like an addressable shift register.

74xx259 has eight individually-addressable bits. http://www.nxp.com/documents/data_sheet/74HC_HCT259.pdf

-- Jeff
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