Questions tagged [65816]
Discussions related to the 65816 CPU.
9
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What is the relation between external clock and internal states in the 68000?
(I'm assuming a memory cycle of 500 ns, without wait states.)
According to the 68000 bus diagram, there are 4 CPU cycles for a memory cycle, so an external frequency of 8 MHz. However, things are ...
22
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7
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Why were there no 32-bit versions of 65xx CPUs, or 64-bit versions of m68k CPUs?
I don't understand why Western Design Center made the 65816 a 16-bit upgrade to the 6502 but Commodore Semiconductor Group/MOS Technology didn't make their own variant & why neither company made ...
13
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answer
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Did Nintendo pay WDC for their use of the 65816 core?
When Nintendo used the 6502 core in the NES (as part of the Ricoh 2A03/2A07 microprocessor and sound generator), they circumvented the 6502's patent protection by disabling the BCD arithmetic. As a ...
21
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What happened to the 65832?
In his June 1985 foreword to Programming the 65816 by David Eyes and Ron Lichty, Bill Mensch expresses his hopes for a 6502-derived 32-bit microprocessor: the 65832. WDC is still thriving, but the ‘...
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Why isn't the WDC 65816 available in "externally" 16-bit versions?
Actually, unless there are actual design notes from WDC available, the
question is really one too long for the title field: "What, precisely,
are the disadvantages of having a version of the WDC 65816 ...
4
votes
1
answer
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65C816: Inputs TTL-compatible?
New 65C816 datasheets say that Vih (for the data bus in particular) is 0.8Vdd, i.e. not TTL-compaible.
Old data sheets (for example, the one published in Apple IIgs Hardware Reference) say that at 5V ...
12
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2
answers
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Early 65C816 CPU's SEP and REP instruction are followed by a NOP?
Why did early versions of the 65C816 CPU need a suffixed NOP to every SEP and REP instruction? I saw comments in some source code pointing at this. Looking around in official WDC's documentation and ...
11
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How does JSR actually work on the 65c816 CPU for the SNES (Super Nintendo)?
Take the following machine code for the 65c816 for the SNES (Super Nintendo):
00000000 ea ea 78 18 fb c2 18 a2 ff 1f 9a 20 fa 80 e2 20 |..x........ ... |
00000010 a9 80 8d 00 21 a9 e0 8d 22 21 ...
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Inserting NOPs to improve IIgs shadow copy performance
The answer to this question discussed a technique on the Apple IIgs for copying memory onto itself. The motivation for the technique was to maximize use of "fast" (2.8MHz) RAM over "slow" (1MHz) RAM ...