Thanks for the new thread Jeff!

Thanks to everybody for the long answers. That cleared up a bunch of stuff for me.



You're right about not fully understanding (which is pretty much why I started this thread). I also wonder if I would have reacted differently if the 8-to-16 bit parts were not based on modes, but part of the opcode-set (say, sta.b for 8 bit and sta.w for 16 bit or something).

Another part of the problem is probably a reluctance to use too many macros while (re-)learning the code. Feels like cheating .

Maybe I just have to actually program a '816 for a bit. Is there any emulator I could try on the Mac or Linux? I only see one on the list ("My Little Simulator - Mertkan YILDIRIMLI") and the link is dead. And I think programming my own emulator is, er, rather above my skill set at the moment ...

Take a look at viewtopic.php?t=1707
Cheers
Ed

Thanks Ed!

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

So how about turning the question around -- is there any reason that a beginner (that would be me) should not start with the 65816 and just use it in 8-bit mode in his designs from the word go?

You could just ignore the bank addresses, after all, and stick to 64 Kb of total memory, as BDD does with POC V1. The price is roughly the same, and that would give you the option of switching to 16-bit mode in code if you want to.

The only thing I can think of is that, if I understand the chip correctly, its 8-bit instruction set is that of a 6502, not a 65c02 (so no STZ or BRA). And I'm assuming that the timing for the data bus is normal (ie, the same as a 6502) in 8-bit mode, so no bank/data duality to deal with on the data bus. Not sure of that, though.

Indeed, it's probably a good substitution, although as you point out there are some things to look out for.

Note, though, that the interrupt handling in emulation mode versus native mode is necessarily different, and it's pretty difficult to cope with either mode, so in a system which has interrupts, an emulation mode program can't just switch into native mode.

So, for more flexibility in software, you're more likely to run in native mode, but possibly stick to 8-bit memory and 8-bit registers.

Similarly, if you switch around the widths of memory or registers, you need to take care when calling from one routine to another that you're not affecting each other's operations.

That is, the chip offers 5 modes of operation, and you have to take a position as to how you're planning to use it. I think this is the most troublesome aspect to get to grips with. I think you need to pick a base mode and mostly stick with it, at least across call boundaries.

Cheers
Ed

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

My SBC-3 & SBC-4 used the 65816 and I switched to native mode on both right after reset and ran 99% of the time using the 8 bit registers and the D register set to $00, keeping zero page at $0000-$00FF. Since most of my code originated on the 65C02 SBC-2, it was relatively easy to port the code with this setup.

If you limit yourself to 64k, you will really enjoy the 65816 and find native mode easy to use.

If you choose to use the bank register, I definitely recommend keeping you code and IO page in bank 0 to start out with. It will make addressing much easier. There are a few complexities when having your OS and/or IO outside of bank 0. It's not a problem, but you need to be very mindful of your addressing modes and it becomes very easy to introduce errors in your code. I can elaborate if you want me to, but I don't want to get you bogged down right yet.

Hope this helps!

Daryl

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scotws asked whether there's any reason that a beginner should not start with the 65816 right from the word go, and the short answer is, no -- no reason. If and when you venture into native mode there'll be some matters to address, and there've been some helpful comments posted in that regard, but right now you can ignore that stuff.

A few minor points. Garth already explained that you'll have all the 'C02 instructions except BBS, BBR, SMB, and RMB. And, interestingly, some of the new '816 capabilities can be used even while still in emulation mode. Also:Software-wise you certainly can ignore the bank addresses and just run in 64 Kb, but AFAIK the duality on the data bus remains. Probably you can utterly ignore this, and not have a problem; just be sure you follow the usual advice about use of bypass capacitors.

OK, venturing beyond "short answer" territory some of us will want to take a closer look. The Program Bank Register and the Data Bank Register are initialized to zero, and will remain zero assuming you remain in emulation mode. But, if I understand correctly, multiplexing will be in effect. That is to say, in emulation mode the CPU drives the value zero onto the data bus in the first half of each cycle. I'm aware that this seems to contradict the following excerpt from section 7.7.2 of the Data Sheet, which states "The following instructions may be used with the emulation mode even though a Bank Address is not multiplexed on the Data Bus [...]" But that's just unfortunate wording, IMO. It's true a bank address is not multiplexed onto the bus, but the value zero is.

If someone wants to ignore hardware aspects of the bank address, it's easy to simply omit the address latch (eg 74xx373) and the extra decoding. But there may still be an argument for including a 74xx245 or similar bus transceiver in the design. This is an inexpensive chip, and the hookup is straightforward. 'C02 designs typically don't require a bus transceiver, but on an '816 it might help forestall problems arising from multiplexing-related bus contention.

cheers,
Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Ah. I had misunderstood that then.



Well, okay then. I'm planning on breadboarding everything first anyway (first parts are in the mail, yippie!), so I think what I'll do is get a 65c02 and a 65816 and fool around with them both before I decide. That way, I can fool around with the bus addressing, too. At the moment, I'm not planning to have IRQ or NMI at all for the first, small, primitive version (just polling the ACIA port for a serial connection), so that wouldn't be an issue. And maybe I will learn to love it .

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

In principle that should work but it assumes that the other devices are sufficiently prompt in obeying their enable signals. Repeating something from the thread Managing the 65816 multiplexed bus...
That's why I say the bus transceiver may be advisable in some cases. It wouldn't be surprising if a beginner planned to run at low clock speeds and to take advantage of slow (inexpensive) memory & peripherals. That's where the problem could arise -- mixing the '816 and its modern process with creaky, old silicon; a 2716 purchased on EBay, maybe. Including a bus transceiver would ameliorate the situation.

cheers,
Jeff

ps- BTW thanks, BDD, for the confirmation re the '816 bus always being multiplexed.

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?