New answers tagged 6502
5
The 64KB of RAM for the 65C102 co-processor is provided by eight MB8264 64k x 1-bit chips. Each chip provides one bit of memory for every address, meaning that all eight chips are used for every memory location. In many instances, the failure of a RAM chip will affect all memory locations (including the 6502's page 0 registers), meaning that the co-processor ...
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The two points are the same. The signal on the SYNC pin is neither the result nor the cause of an opcode fetch; it's internal signals in the chip that cause both the SYNC pin to go high and the data from the next memory fetch to be treated as the next opcode to execute. The Wikipedia article and the referenced patent are both talking about this separate ...
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While Wilson and Janka already explain the arithmetic and 6502 related (*1) implication, I somehow get the feeling this question is not about the 6502
Behavior of the zero and negative/sign flags on classic instruction sets
but rather some generic, absolute meaning.
I'm very curious, cross-architecturally, how this has varied.
There is no variation, ...
11
Neither. In the 6502, the Z flag is set if there's an all-zero pattern on the internal data bus in the last instruction cycle and cleared if it isn't. This means specifically instructions as PLA or TAX affect the Z flag. On the 65C02, e.g. PLX does, too.
You can see this from the CMP, CPX, CPY, BIT instructions, which store nothing.
Same for the N flag, it'...
5
In the case you describe, the 6502 will set the Zero flag (in other words, the Z flag will be one if the operation left the accumulator equal to 0 mod 256). That's convenient, because usually a programmer is interested either in Z, to test for an actual zero condition, or in C, to test for a carry.
The Z80 works in the same way.
My understanding is that it'...
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There were two major reasons:
1: On introduction, the 6502 (at $25) was considerably cheaper than its nearest competitors; at the time, those were the 6800 ($175) and the 8080 ($179); the Z80 would not be released until the following year, and even then its initial price was $200.
2: Despite its low cost and simplicity, the 6502 was relatively fast for a ...
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Probably the most modern BASIC available for the 6502 - though it requires a 65C02 - is Acorn's BBC BASIC IV as released for the BBC Master. It can be ported to other 65C02-based 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. The standard version occupies ...
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Steve Wozniak wrote most of his software to be compact rather than fast, reflecting the constraints of affordable memory hardware of his time. That often resulted in contortions that made it run considerably slower than a speed-optimised implementation, such as the extensive reuse of the FMUL subroutine mentioned.
Home micros sold before 1980 typically ...
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The June 1983 issue of Softalk magazine carried an article on the 65C02. It opens as follows:
This month's discussion deals with a new version of our beloved 6502 microprocessor known as the 65C02. Although the chip has just been released within the last few months and has yet to find its way into the mainstream of computers, it seems likely that we'll be ...
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