6502.org

Wikipedia has a brief comparison of a long list of CADs, many of them free, at https://en.wikipedia.org/wiki/Compariso ... A_software.  See also http://pcbshopper.com/cad/ for some info and reviews on free PCB CAD.  You might find a few that will run with 256MB of RAM.  I still use an old DOS-based CAD that runs with 1MB (not GB!) of RAM, for reasons that would not apply to most people.  But like every other CAD I've tried the demos of, it has major things about the schematic capture portion that I greatly dislike, so I still do my schematics by hand.  The most complex board I ever laid out with it had 12 layers and about 500 parts, in 1994 on a '286 with 1MB of RAM and a 32MB (not GB) hard disc, and I did not run out of memory.  How's that for efficient memory usage?! (I never did fill up that hard disc either until I tried installing Windows, and suddenly I needed several times that much disc space just for the OS.)

OK, Fixed the random x'es
cleaned up MOST of the schematic and labeled everything: Aaaand here's the Gray-scale: (Please Include the page number where the issue is , make it a lot easier for me !!)

Well, there's still many areas of concern with this...

1- You have inconsistent part labeling, some chips are U-, some are X- and several are using an alpha character (which denotes, e.g., multiple gates in a single chip). Chips like a 74HC138 will never have an alpha character, as it's a single logic device.
2- You still didn't add the 1Meg resistor in parallel with the crystal for the 65C51.
3- The diode on page 1 (D3) appears to be a pull down via U25 from page 2. As the 74AC00 (U9d) is not an open collector device, you will possibly have U25 and U9d trying to hold the line at opposite voltage levels.
4- Your port selects on page 3 (U17/U18). Are you intending for these to be active high or active low? In general, most designs have select lines which are active low. The 74AHC138 has active low outputs.... you're inverting them to active high.
5- Flash memory device U8 (page 1) shows a Reset line as pin 1. Is this correct? Exactly what part is this?
6- Page 1, the R/W line from the CPU is not connected to R/W signal label.
7- Page 1, the VDA/VPA lines from the CPU are not connected to anything I can see...
8- The DB9 serial connector on page 3. Is your intent to use the async port as a serial attached console? By definition, the DB9 pinout denotes a RS-232 port, which is not TTL levels. There are numerous ways to attach as a console... you should look into them.
9- Page 2, U20/U27... you're using 3 NOR gates (74HC02), but showing 2 different chips (where one will suffice). You're also using what appears to be a NAND gate symbol, not the NOR gate symbol. Perhaps it's the software you're using.

From your original schematic, you've deleted many chips and logic bits, but you haven't really gone thru the schematic to re-label the parts to ensure you have a workable part list and ability to put this into a PCB. I would also say it's somewhat incomplete as a design. As you've added a GAL, have you looked into a configuration for this to see if it can be programmed and simulated successfully?

FloobyDust,

The logic chip Alpha character is just more goofiness i have yet to resolve, fro now were both going to just have to deal with it (Sigh...) .

I did want to have my Port Selects active low, thank you for pointing that out.

The flash memory is a ATMEL AT49BV002ANT (i Thought I labeled it, Guess not , OOPS!)

How should I connect My VDA and VPA Signals ?
as for the Serial port, its just the connector im using, as ill probably just run it through an aurduino or something to get actual Serial output. (and no i dont actually pan on using it as a console, I plan on using a Propeller 2 chip for VGA graphics, but its not in my software's part library and i have yet to make the 100 pin tqfp package and label all the pins, as well as add level converters for the interface.)

I added the resistor and am double checking the Logic components are all denoted with U and Not x, and the Nor gates were Supposed to be NAND but I guess trying to tell at 1 am with out glasses wasn't a good idea.


I dont think the GAl should be an issue, as its acting as a Rom (basically) with clocked inputs, as its used on the Bank addresses to decode the various things in that area ( E.G., The Prt select Logic, Add on ram, ETC.) .

Thanks for the help and putting up with my Software's (And My Own) Goofiness.

more updates to follow.....

You might want to consult the datasheet for the ATMEL AT49BV002ANT. Two things stand out, first, this is a battery voltage part, 2.7V - 3.6V. As you're using a 5-volt supply, expect it to blow quickly. Second, (according to the datasheet), pin 1 should be a no connect on the part you've referenced.

As for the VPA/VDA pins, you should look at some existing 65C816 designs and read thru the datasheet for the W65C816. I strongly suggest you look at BDD's POC design (he attached it earlier in this post) and also take a look at WDC's SXB that uses the W65C816. Both show how to use these signals.

If you don't really have a use in mind with the 65C51, why bother adding one? If you need a serial port, just use a MAX23(x) level converter along with a properly functioning async controller.

PS - BDD posted while I was typing... look at his attached POC130.pdf

hi all,
was just redesigning the schematic in Kicad 5.1 and was curious as to what part I should use to convert my 5v data/ adress bus signal into a 3.3v for my propeller chip (video and audio generator.)

Thanks in advance!

Hi Kuzailongmane,

The Propeller P8X32A is not 5V tolerant so voltage-level translation is definitely needed to interface it into a 5V circuit.

If the propeller only receives signals from the 5V side (i.e. every P pin is configured as in input) then it is fairly easy. Placing a 5V tolerant TTL bus transceiver between the 5V signals and your propeller will sort you out. Something like the 74AHCT245 or the 74AHCT541 (note the highlighted 'T's indicating they use TTL voltage levels). Both of those are available in DIP packages. Assuming a 16bit address bus and an 8bit data bus you'll need three of them as they're 8bits each.

The '245 has a direction pin but you'll wire it for only one direction for everything connected to input P pins on the propeller. The '541 can only ever send a signal in one direction.

If the Propeller is talking back out to the 5V side of the circuit then it is more complicated. For that you'll need 3.3V to 5V voltage translator like the 74AHCT4245. The '4245 like the '245 has a direction pin so you must tell it which way it is sending the signal and that is going to depend on how you're using it in your circuit.

I can't find any 74AHCT4245s for sale anywhere reputable (nor can I find any HCT versions at all) so you may have to use a 74LVC4245 instead. I don't believe those exist as DIPs so if you're using a breadboard you'll need to solder the surface mount job onto a breakout board.

Cheers,
Andrew

ps: I noticed in your schematic you have a pair of HCT595s talking out to your 5V data bus. That's probably not going to work, you'll need HC595s instead.

74LVC might be worth a look if it meets your timing constraints: e.g. https://eu.mouser.com/datasheet/2/916/7 ... 578860.pdf

Somewhere in the LVC range I've seen bus interface parts with two Vcc pins, one for each half, but I can't immediately locate them.

Neil

There's a note on the P8X32A datasheet that says: "I/O pin voltages with respect to Vss may be exceeded if internal protection diode forward bias current is not exceeded."

So putting a 4K7 series resistor between the 5v signal and the 3.3v input pin saves the need for any level shifting down to the propeller. A 74LVC245 powered from the 3.3v supply has 5v tolerant inputs if you want to use that instead of resistors. As a 3.3v device it will be driving the propeller at a safe voltage.

The 74HCT245 is powered from 5v, but becuase it has TTL inputs, will level shift the 3.3v output from the propeller to 5v CMOS for a 65C02 or 65C816. You don't want that chip driving the propeller inputs direct, because it outputs 5v.

Both of those 245's would be one way level shifing as the ouput drive will be at the supply level for the device.

I won't link the projects I've done level shiting this way as the're Z80.

A very good catch thanks, and why I should always double check datasheets before posting. You're right the HCT versions will output up to 4.5V, completely negating saving the P8X32A from 5V with the down translating that it is not doing. The 3.3V LVC 245 is the way to go to protect the Propeller if want you use a bus transceiver to do it.

Updates!



so after updating to Kicad 6.0 and getting a new windows machine i have good and bad news:

good news:
No More Target! 3001 funkiness with inconsistent part labeling
no more random export funkiness
figured out what level shifters ic's I'm going to use
Bad news:
I have no idea how to export the file into a monochrome pdf (sorry BDD) or pdf in general
As kicad cannot import .tar310 files I have to recreate the schematic and PCB from scratch


thank you all for your support and patinece and i will hopefully have the fresh schematics done soon!

great to see you#re making progress, even if it means redoing all schematics from scratch...

exporting to PDF in kiCad is pretty straightforward.
with the schematic editor open go to "file" -> "plot", which opens a new window.
in said window you select the "output format" to be PDF, the "output mode" to black and white, and tell it where to save the file (you can use a single backslash to have it save to the project's directory)

If you're going to redo your schematics, consider using bus wiring for the address and data busses. It will make the schematics more readable. Here is WDC's 816sxb board schematic as an example.