A new article about 6502

White Flame · Post by **White Flame** » Thu Sep 10, 2020 9:10 am

GARTHWILSON wrote:

and the (ZP,X) is tremendously valuable in dealing with a virtual stack where some of the cells on the stack are addresses and X is used as the virtual-stack pointer. I definitely use X more than Y. Even for hardware-stack addressing, there's the TSX and TXS, but no equivalent for Y.

And even if you're exclusively using Y indexing, that means you'll always be using X for a loop counter.

BigDumbDinosaur · Post by **BigDumbDinosaur** » Fri Sep 11, 2020 3:34 am

GARTHWILSON wrote:

and the (ZP,X) is tremendously valuable in dealing with a virtual stack where some of the cells on the stack are addresses and X is used as the virtual-stack pointer.

Not to mention using (<dp>,X) for selecting UART channels to process.

JimBoyd · Post by **JimBoyd** » Fri Sep 11, 2020 8:29 pm

brain wrote:

tiny is better. But, it's still an awfully loaded term. Minimal, or nominal, or half hearted I think would be better (and more nuanced). tiny and microscopic are boring words.

Incremental?

brain · Post by **brain** » Sat Sep 12, 2020 1:55 am

JimBoyd wrote:

brain wrote:

tiny is better. But, it's still an awfully loaded term. Minimal, or nominal, or half hearted I think would be better (and more nuanced). tiny and microscopic are boring words.

Incremental?

Also a good choice and somewhat more neutral.

Jim

1024MAK · Post by **1024MAK** » Sat Sep 12, 2020 2:32 pm

I’ve not read the linked to article. But one thing that is more important than features alone, especially in the 1970s and 1980s, was getting the price right (as in low) with just enough features so that it sells.

This was when complex highly integrated circuits were expensive. Especially microprocessors and RAM chips.

And microprocessors designed for use in embedded systems (which was the original market for the NMOS 6502, and also for the Z80) did not need anything that would require any extra cost.

Despite not being designed for use in home computer systems let alone business systems, the 6502 and the Z80 ended up in business computers, educational computers and home computers as well as arcade machines. But also in their original market: embedded systems.

Why, because they were low cost solutions.

Now, looking back (in hindsight), it’s easy to say that there should have been improved versions made. But at the time, when the fabs were having trouble keeping up with production, that’s not really thought about.

Similarly, computer manufacturers are not going to spend too much time and money designing a new computer whilst they are selling their best selling models by the truck load. Hence low or no demand for anything better in terms of the microprocessor.

And then technology moves on and someone else is now working on 16 or 32 bit microprocessors (look up the dates for the 68000 and the 8086 and then look at when the first 16/32 bit computers were first sold). At the same time, most of the computers that these chips (6502, Z80) are being used in, are undergoing cost reduction measures by the manufacturers so that the older model of computers can stay price competitive. Not a good market for a new more expensive eight bit microprocessor... so even less call for a more expensive eight bit souped up microprocessor.

As it happens, because both the 6502 and the Z80 got CMOS versions, they both live on. Because they can be used in low power devices.

Of course, if a significantly faster and/or significantly more capable eight microprocessor that was backwards compatible had been made at low cost back in the mid 1980s, people may well have wanted it in their computer systems.

The bit about the Acorn BBC Micro (also known as the model B). Acorn did design and manufacturer an export version for sale in the U.S.A. As far as I know, they were not blocked or locked out as such. In their home market (the U.K.) these machines were already in the expensive segment of the home computer market. Lower cost Commodore 64 and Sinclair ZX Spectrum computers outsold the Acorn models by a considerable margin, and don’t forget there were many other home computer manufacturers at the time as well, some of which were also undercutting the cost of a BBC Model B machine.

The U.S.A. model included as standard, what were optional features (see here) on the models sold in the U.K., plus all the extra screening added to the cost of each machine. So my feeling is that they priced themselves out of the market. They were never going to really compete with the C64 for a home computer. And if you wanted a more business like computer, then a business would be more likely to either buy and use a CP/M machine or a IBM PC.

The only lock or block really, was the interference suppression requirements (screening and testing) that were required before it was legal to sell systems in the U.S.A.

This was also part of the reason that other U.K. home computer manufacturers had difficulty trying to enter the U.S.A. market.

Interestingly enough, Acorn did push 6502 system functionality more than most home computers in that it’s ‘main’ 6502 normally runs at 2MHz when accessing ROM or RAM. The optional second processor expansion runs even faster at 3MHz. Later on the (internal) second processor board for the Master 128 (the machine is then known as the ‘Master Turbo’) runs at 4MHz. And the Master series machines use a CMOS 65C12 and use the extra instructions to improve the OS code.

By the time of their last eight bit machine (the Master Compact), the OS and BASIC had been improved significantly, in part due to using the 65C12 (and also by general code improvements). See the section under “Performance” in this review (yes, it’s obviously biased). However by now, eight bit machine sales were falling, as most people wanted the new 16/32 bit machines...

Mark

Martin_H · Post by **Martin_H** » Sat Sep 12, 2020 4:33 pm

GARTHWILSON wrote:

and the (ZP,X) is tremendously valuable in dealing with a virtual stack where some of the cells on the stack are addresses and X is used as the virtual-stack pointer. I definitely use X more than Y. Even for hardware-stack addressing, there's the TSX and TXS, but no equivalent for Y.

A +1 to (ZP,X) as well. Last year I wrote a toy compiler for a Scheme like language, and I used that for reference arguments.

Looking at one of my common macros modules. I use ",x" 68 times and ",y" 4 times. So I'm really partial to it. But I stole my 6502 assembler style from Forth, so no shock there.

Pairing X and Y together can be really powerful. Such as copying a data stack cell to a location via a pointer. There you use the Y rather than alter the pointers contents.