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- Comparing raw performance of the Z80 and the 6502
This is actually more true on the 6502 (so long as you tri-state its address lines during ϕ1) Essentially, the 6502 needs "double-speed" RAM because it does all RAM access during only half the cycle (ϕ2) and leaves it unused the on the other half (ϕ1) ϕ1 was often used for cheap, interference-free video framebuffers and RAM refresh
- Why did so many early microcomputers use the MOS 6502 and variants?
Second, the aggressively low price point of the 6502 Chuck Peddle's team developed the 6502 to be a low-cost, compatible, Motorola 6800 "killer", much the same way as Zilog did in targeting the Intel 8080 with the Z80 Again, Jack Tramiel's willingness to far undercut his competition kept the 6502 as a relative bargain among the early 8-bit
- What is the MOS 6502 doing on each cycle of an instruction?
Assuming you’re asking: what can the 6502 be seen to be doing by an external observer, then the data sheet has a full breakdown of bus activity per cycle per addressing mode; that was long ago transcribed into ASCII form by the Commodore community and is now often sourced from that 64doc txt
- 6502 - Transistor-level schematic of 65C02 - Retrocomputing Stack Exchange
I'll note, however, that the 65C02 schematic design is not significantly different from the original NMOS 6502 It might be a good exercise for your students to convert NMOS to CMOS There is an educational IP license mentioned on the WDC site that you might look at
- What was the 6502s reset behaviour when the RDY pin was low
Compare figure 1 13 below, showing no bus activity before Phase 2 goes low for the fetch of the reset vector However, mind SYNC (6502 specific) going high during the 3rd cycle of the sequence (I have no idea what the implications of RDY = 0 for this SYNC spike might be )
- Modulus arithmetic on the 6502 - Retrocomputing Stack Exchange
Here's a shorter solution than wizzwizz4's: SEC LDA x SBC modulus ADC y BCS end ADC modulus end: The idea is to bias the inputs so that the addition overflows just when the modulus needs to be subtracted
- 6502 - Why dont all Absolute,X instructions take an extra cycle to . . .
Therefore the 6502 always takes a 'penalty' read cycle with an (probably) incorrect address before performing the final write Interesting enough, the little-endianness of the 6502 made such a cycle-saving possible Were there big-endianness, like in the 6805, there would always be a penalty in index addressing, as it happens in the 6805 itself
- 6502 - Why does the BRK instruction set the B flag? - Retrocomputing . . .
But the 6502 already has the ability to read from three different vectors when the interrupt happens; Almost, but different, and very cleverly made to reduce the needed hardware to almost zero and intuitively, supporting four vectors is no harder than supporting three It is, as generating addresses does need some logic
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