Jun 8, 2020 · There are, however, minor functional differences between the 6502 and the 65C02. If your application relies on undocumented opcodes, or makes creative use of certain bugs in the 6502, the 65C02 may not work for you. On the hardware side, three pins have been re-assigned in the WDC 65C02, compared to the 6502 and earlier (Rockwell) 65C02s.

May 21, 2022 · 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.

May 14, 2017 · 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 ...

Dec 13, 2020 · 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.

Feb 7, 2021 · 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.

Mar 14, 2022 · 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.

Feb 9, 2018 · The 6502 has a limited form of pipelining where it fetches the next instruction on the last cycle of the current instruction. Thus the PD register would be needed to latch the next instruction while the IR is still holding the previous one and controlling the final cycle of execution. –

Apr 3, 2024 · 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.)

Nov 21, 2016 · The 6502 excels at accessing tables which are 256 bytes or less since its indexed addressing modes include "free" address arithmetic. I've written wave-table synthesis code for the 6502 which takes 46 cycles of every 76-cycle scan line, and uses 20 different pointers for audio in each group of four scan lines (plus more for video). –

Apr 24, 2024 · 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.