6502 basic

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6502 basic

Update : The source is available at github. If you disassemble a single binary, you can never tell why something was done in a certain way.

The MOnSter 6502

If you have eight different versions, you can tell a lot. This article also presents a set of assembly source files that can be made to compile into a byte exact copy of seven different versions of Microsoft BASIC, and lets you even create your own version.

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FP : Whether the 6 digit or 9 digit floating point library was included. Download the assembly source code here: msbasic. You can build the source by running the shell script make. This will create the seven files cbmbasic1. Make sure to read on to the end of the article, as it explains more about the source and what you can do with it.

While most OEM versions were heavily modified in its user interaction startup screen, line editing…most of the code was very similar; some functions were even never changed for any version of BASIC.

No OEM ever came back to Microsoft for updates, except for Apple and Commodore, which both synced once each, up to the bugfixed version 2.

Speaking of patches: Commodore BASIC 1 has been binary patched a lot: There are six patch functions appended to the very end of the interpreter image that work around miscellaneous fixes. This is what one of these calls into a patch function looks like:.

Some of these patches are in generic code, and some in Microsoft-specific code. Later fixes in generic code are not necessarily identical to these patches.

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So this indicates that Commodore wrote the fixes. But it is unknown why these additions were done in the binary as opposed to the source: Commodore had the source and made lots of additions to it. Maybe it was just more convenient to patch the binary for debugging at some point. Ohio Scientific sold a wide series of based machines for several years, but they all shipped with the same version of 6 digit BASIC bought from Microsoft in Ohio Scientific only made minimal adaptions for their computers, and added no extensions.

The code to print this string and adjust memory layout accordingly is not included.

Your Guide To Building A Homebrew 6502 Computer

Without the extra string, they could have saved 21 bytes. On startup, it printed:. The encoded XOR 0x87 text was hidden in some floating point constants and never addressed. Compared to 1.

6502 basic

CHRGET is supposed to set the zero flag on the end of an instruction, which can be end of line 0 character or a colon. The original code wanted to check for an empty line and got the first character, and went on reading another line of it was empty — but a colon as the first character had the same effect.

Version 1. On 9 digit BASIC, one extra byte had to be copied, but the start index was not changed, so the last digit was omitted.This is the original source code of Microsoft BASIC for with all original comments, documentation and easter eggs:.

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A set of macros developed by Paul Allen allowed MACRO to understand and translate assembly, albeit in a modified format to fit the syntax of macros, for example:. MACRO did not support hex numbers, which is why most numbers are in decimal format.

In the floating point code, all numbers are octal. It has one of the following values:. The target defines the setting of the configuration constants, but some code is also conditionally compiled depending on a specific target.

What is interesting is that initially it was Microsoft adapting their source for the different computers, instead of giving source to the different vendors and having them adapt it. Later, the computer companies would get the source from Microsoft and develop themselves — source code of the Apple and Commodore derivatives is available; they both contain Microsoft comments.

By the way, the numbering of these targets probably indicated in which order Microsoft signed contracts with computer manufacturers. When targeting a real machine, the binary could be created by simply extracting one byte from every PDP word. In the case of targeting the simulator, the code created by the assembler could just be run without modification, since every emitted PDP instruction was constructed so that it would trap — the linked-in simulator would then extract the opcode from the instruction and emulate the behavior.

While this trick was mostly abstracted by the unreleased macro package, its workings can be seen in a few cases in the BASIC source. Instead of just emitting 0x24 or 0x2C, respectively, it combines it with the octal value of to make it a PDP instruction that traps:.

With this information, we can reconstruct what the set of macros, which is not part of this source, probably looked like.

These are the first ports to specific computers, and also the cleanest, i. This is the WAIT instruction:. But on Commodore, we have this code hidden near the top of the floating point math package — close enough so the BEQ can reach it, but inside code that is least likely to get touched:.

6502 Computer - Running Basic on Working Board

Also note that all numbers here are octal, since this code is in the floating point package. First of all, the final line here removes ZSTORD from the list of symbols after the second pass, so that Commodore would not notice it in a printout of all symbols — very smart! The encoded string is hidden as two extra 40 bit floating point numbers appended to the coefficients used by the SIN function:.

Also note that these constants are not conditionally assembled! All versions built since the Commodore easter egg was introduced also contained these 10 bytes — including BASIC for the Motorola ! Here are the headings:. People have since wondered what runtime vs. The last entry in the change log has a date of Ok, we connect an 8-bit microprocessor to Arduino Mega, but how does it really work? Arduino Mega is connected to the as follows. Internally it seems everything happens with respect to CLK2 edges however, the internal delay between CLK0 and outputs is small and for our purposes we will assume all clocks edge are aligned and refer to CLK0 output from Arduino into Since all activity happens on clock edges, setup and hold times are the minimum time required to get the data ready before the clk edge setup time and to keep it constant after the clock edge so there is no corruption while latching is completed hold time.

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To achieve that the Arduino code uses timer1 interrupt. Since timer fires at fixed times, it is important the timer handler completes before the next interrupt. This is the excerpt from the Ardino code. Apple I has a PIA to handle keyboard and display.

After reviewing the monitor code, I cheated and emulated just enough to get keyboard and display working. The beauty of software is you can anything you want.

Last, since you can use existing arduino shields like display, sdcard, audio, etc.The design team had formerly worked at Motorola on the Motorola project; the is essentially a simplified, less expensive and faster version of that design. When it was introduced inthe was, by a considerable margin, the least expensive microprocessor on the market.

It initially sold for less than one-sixth the cost of competing designs from larger companies, such as the or Intel Its introduction caused rapid decreases in pricing across the entire processor market. Along with the Zilog Z80it sparked a series of projects that resulted in the home computer revolution of the early s.

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Soon after the 's introduction, MOS Technology was purchased outright by Commodore Internationalwho continued to sell the microprocessor and licenses to other manufacturers. In the early days of theit was second-sourced by Rockwell and Synertekand later licensed to other companies. In its CMOS form, the 65C02which was developed by the Western Design Center WDCthe family continues to be widely used in embedded systemswith estimated production volumes in the hundreds of millions.

The was designed by many of the same engineers that had designed the Motorola microprocessor family. The chip layout began in latethe first chips were fabricated in February and the full family was officially released in November Motorola's "total product family" strategy did not focus on the price of the microprocessor, but on reducing the customer's total design cost. They offered development software on a timeshare computer, the " EXORciser " debugging system, onsite training and field application engineer support.

Peddle, who would accompany the salespeople on customer visits, found that customers were put off by the high cost of the microprocessor chips. At that time, Motorola's new semiconductor fabrication facility in Austin, Texas, was having difficulty producing MOS chips, and mid was the beginning of a year-long recession in the semiconductor industry. Also, many of the Mesa, Arizona, employees were displeased with the upcoming relocation to Austin.

Motorola's Semiconductor Products Division management was overwhelmed with problems and showed no interest in Peddle's low-cost microprocessor proposal. Eventually Peddle was given an official letter telling him to stop working on the system. The new group vice-president John Welty said, "The semiconductor sales organization lost its sensitivity to customer needs and couldn't make speedy decisions.

Peddle began looking outside Motorola for a source of funding for this new project. Sevin, but Sevin declined and later admitted this was because he was afraid Motorola would sue them. While Peddle was visiting Ford Motor Company on one of his sales trips, Bob Johnson, later head of Ford's engine automation division, mentioned that their former colleague John Paivinen had moved to General Instrument and taught himself semiconductor design.

He had since moved on and was doing some very interesting work on calculator chipsets at a new company he formed in Valley Forge, Pennsylvania.

The source code behind Microsoft BASIC for 6502 comes to light

Allen-Bradleya supplier of electronic components and industrial controls, acquired a majority interest in Mike Janes joined later. Of the seventeen chip designers and layout people on the team, seven left. The goal of the team was to design and produce a low-cost microprocessor for embedded applications and to target as wide as possible a customer base. Chips are produced by printing multiple copies of the chip design on the surface of a "wafer"a thin disk of highly pure silicon.

Smaller chips can be printed in greater numbers on the same wafer, decreasing their relative price.In his guide to building a computer, [Garth] goes over all the basics — what you want the computer to do, how to decode addresses, and other important technical requirements for getting a homebrew project running.

There are a ton of tutorials on the I like thebut among other perks the 65c latest-gen features a linear, 16MB address space. The Programming Model is a major step up from the — with a full bit ALU for starters, and you can do ish tricks such as indexing into the stack to reference an indirect pointer to an operand in memory. I might as well say a bit CPU is better than the Comparing an 8-bit to a bit is apples and oranges. The is the best 8-bit CPU.

The is nearly as easy to use as the or The same cannot be said for modern and bit processors. It has been a couple of decades since I even looked at the different types of computer architectures.

Does anyone have any advice in choosing an architecture? It just depends on what you grew up on, really. This includes not just the CPU architecture, but memory, graphics, sound, storage mmm, cassettes! Thanks so much for reminding me : …. There is a 32bit already.

Microsoft BASIC

My MPU of choice is the much more versatile 65C Is it really fair to compare the 8-bit to the bit ? If you think it is, then it is fair to say any bit or bit CPU beats the Several of the circuits have accompanying example code. A couple more major features have been added to the site since the primer was posted.

6502 basic

See how. The other is on program structures in 65c02 assembly, through macros, enabling you to more quickly write clearer, more bug-free and maintainable code and get rid of most of the labels, in most cases with absolutely zero penalty in memory usage or execution speed.

6502 basic

I should be adding more to the looping controls there soon. The next major feature will probably be a primer on stacks plural, ie, not just the native hardware stack and the non-obvious things that can be done with it, but also auxiliary stacksagain with a focus on 65c02— so stay tuned.

I add things to the site every few days. Most additions are minor, as I am taking some time off from writing to work on hardware; but I have a few more major features in mind to add in the future, including one on self-modifying code. If you have things you would like to see make it into that one, please email them to me, at wilsonmines dslextreme. I will give you credit.

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Learn more. Report comment.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear.

It only takes a minute to sign up. I'm ultimately interested in seeing if there is a way to make a fairly universal BASIC for the platform that is a modern improvement on the MS standard.

I know there are a number of examples like BBC and TURBO that have significant performance improvements, as well as complete re-implementations like FastBasic that everyone should look at. And then there's the various potential improvements seen here, especially supercat's remarks on strings. The syntax is familiar to Pascal, C, and assembly programmers. It can be ported to other 65Cbased hardware by implementing a few of the MOS API entry points it relies on, and dummying out the rest; several people have done so for home-built SBCs.

I thoroughly recommend digging out a BBC Master emulator and playing around with it. I do not believe it's a port from a vintage BASIC, but recreated out of whole clothbut it seems pretty mundane and conventional. It was noted for having some interesting features. It's actually quite powerful. If you want to try your own, figure out how you can design things to deal with the following basic pun intended operations:.

The last operation is probably the most performance-sensitive, but you should try to make the first one be fast as well.

The second probably isn't likely to matter from a performance perspective, but you should ensure that the amount of code required to accomplish it is reasonable. Having an input scanner convert something like.

While converting expressions to prefix or postfix form may slightly expedite processing, keeping them in infix will make listing much simpler. If you store strings literal or otherwise with a length prefix and ensure that each string in memory takes at least three bytes total perhaps by saying that a string pointer whose MSB equals 1 should be interpreted as a single-byte string that may facilitate garbage collection by allowing relocated strings to be replaced by a pointer to their new address.

The Oric 1 and Oric Atmos had a good full featured basic language for the day. Both machines used the A in the old standard 40 pin package. Back in the day the early 80'sa friend of mine disassembled the machine code from the ROM and then extended many of the commands and added a few new ones. As I recall, the programming had to be very creative since the ROM was only 16K and the OS, as it was, only just fit within a few bytes.The code was posted on a Korean-language site and, subsequently, a nice analysis and breakdown was provided by Michael Steil, a self-described operating system hacker and CISC enthusiast.

That same year, MOS Technology created the microprocessor as a cheaper alternative to other microprocessors of the day.

The would eventually be used in a number of popular computers, such as the Apple I, the Apple II, Commodore VIC and 64 systems, as well as gaming consoles such as the Atari Initially, MOS created their own computer board using thecalled the KIM-1, which hobbyists could use to build their own system.

In his analysis of the code, Steil concludes the source of it was someone at Apple, and that based on the change log and the comments, this was version 1.

Steil also points out many interesting things about the code, such as:. He also provides great detail on the code structure and many other interesting finds. Exposing the source: 16 pieces of classic software whose code is now accessible. Follow Phil on Twitter at itwphiljohnson. Konstantin Lanzet. Monte Davidoff is credited with writing the math functionality e. Related: Software Developer.


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