I suspect I already know the answer but is there a counter, like a '161 or '163 or similar, that has both the ability to parallel load and the ability to set its output to high impedance? And it must be fast.

That would be so useful for using counters for memory address that I don't always want on the bus.

Looks like the '469 is one such, but having found it there's the question of availability.
https://en.wikipedia.org/wiki/List_of_7 ... d_circuits

Edit: perhaps the '461 too.

Here are some 8-bit counters that may fit the bill, but they have TTL-level outputs; also, the prices and availability are poor.

You could also use an EPROM and a '574 to generate a count sequence. But a PAL or CPLD would be faster.

-- 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

Thanks BigEd and Dr Jefyll!

A pity about the availability (and price) because otherwise those are some really interesting chips.

Particularly the '461would have been perfect.

Well, if it was bit faster. I don't suppose anyone has a chip fab lying around and can produce this in LVC?

And whilst I'm wishing, maybe an internal register like the' 590. And up/down too

But seriously I suppose few industries would use discrete ICs nowadays. I guess it's all (fairly) gone FPGA / CPLD

My guess is, using a standard counter and a separate register IC is not feasible eg due to board space?

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/

Curious about this, I remembered there is a 4-bit counter with parallel load in the GALasm package, so I modified this to be an -bit counter, but get an error in the 7th bit, (too many product terms) so it may be possible by re-arranging it or using a spare pin as a temporary (or limiting it to 7 bits?)

Or using another tool - this was targetting a GAL 22v10.

-Gordon

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--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

The short answer is laziness: it's more ICs to solder and route, more testing and more chance of a mistake. The longer answer is I'm trying to reduce the ridiculous number of ICs I need in my build. Each one has complexity as it adds propagation delay (think two 4bit '161s into a an 8bit '541 and multiply that out to 24bits) and potentially more current draw and/or load on whatever is driving it. I might end up amplifying ringing that wouldn't happen in a single IC, need impedance matched resistors and more decoupling caps. Basically it's just more to think about in a project that, while a hell of a lot of fun, has gotten wildly complex.

And expense. Which makes the 22v10 almost a contender. The price of two 74LVC161s and a 74LVC541 is only a bit cheaper than a single ATF22v10. A bit off topic but I don't think I understand the 22v10 (specifically the ATF22V10C) as even at 100Hz frequencies the current draw sits around 150ma per chip - which strikes me as quite high. And means if I use a significant number of them I'm pulling amps.

[edit]I forgot to mention that the 74FCT191 exists and still readily available, reasonably cheap and fairly quick.
But it's also huge! Can't have everything I suppose [Further edit]The 73HCT193 is the cheap IC, not the FCT. Oops

I have 2 Lattice 22v10's on my '816 board and the idle current draw is about 150mA. The board is running at 16Mhz and also has an ATmega 1280 and an SD card.

-Gordon

_________________
--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/