Like its precursor, the Motorola6800 (but unlike Intel8080) the 6502 has very few registers. There was one 8-bit accumulator register (A), two 8-bit index registers (X and Y), an 8-bit processor status register (P), an 8-bit stack pointer (S), and a 16-bit program counter (PC).
Danny Spracklen: Yes, the instruction set was a little more efficient, I think, and more- it was more, if you could say, RISC like. ...
It was a simpler instruction set, but it actually- the cycle times on the individual instructions were very fast, like one microsecond, instead of like 4 or 5 microseconds, on the Z-80.
Kathleen Spracklen: Yes. And it had the short branch. You can’t underestimate the value that the short branch offered. They had the ability- if you could branch within a one byte distance of where you were, and using it as a sign number, positive or negative, you had an extremely fast branching instruction. So if you could make loops very, very small and tight, you could really run with high, high speed.
The TurboKit TK20 by German engineering company Schaetzle+Bsteh was a discrete 6502 compatible 18 MHz high speed CPU with own fast shadow memory build from more than 100 integrated circuits, dedicated for general purpose and chess computers with 6502 processor, connected via a ribbon cable to the 40 pin processor socket of the host system [4][5][6]. The TK 20 was used by Ed Schröder with his dedicated Rebel programs at the WCCC 1986 and various World Microcomputer Chess Championship, and also by Ulf Rathsman and his Y! programs. Further, the dedicated Saitek Leonardo Turbo mini series was extended by Schaetzle+Bsteh with an 18 MHz integrated TurboKit [7].
Table of Contents
Register Files
Like its precursor, the Motorola 6800 (but unlike Intel 8080) the 6502 has very few registers. There was one 8-bit accumulator register (A), two 8-bit index registers (X and Y), an 8-bit processor status register (P), an 8-bit stack pointer (S), and a 16-bit program counter (PC).Endianess
Unlike Motorola 6800, the 6502 is a little-endian processor, concerning the byte-order of 16-bit words in memory.Quotes
By Dan and Kathe Spracklen from their Oral History [2] on the advantages of the 6502 compared to 8080/Z80 while porting Sargon:you could say, RISC like. ...
It was a simpler instruction set, but it actually- the cycle times on the individual instructions were very fast, like one microsecond, instead of like 4 or 5 microseconds, on the Z-80.
Kathleen Spracklen: Yes. And it had the short branch. You can’t underestimate the value that the short branch offered. They had the ability- if you could branch within a one byte distance of where you were, and using it as a sign number, positive or negative, you had an extremely fast branching instruction. So if you could make loops very, very small and tight, you could really run with high, high speed.
Architecture
TK20
See also
Manuals
Selected Publications
[9]For instance, how to flip the board in 6502 Assembly [10] :
Forum Posts
External Links
6502.org Forum
References
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