
Verilog 6502 (2016) - tomcam
http://www.aholme.co.uk/6502/Main.htm
======
sehugg
_Internal busses are precharged to $FF during Φ2 and then connected to one of
the ALU input latches in the immediately following Φ1, during which the nodes
are floating. This forces $FF onto the ALU input by swamping it with charge
from physically larger nodes. A register (X, Y, SP or PCH) is routed to the
other ALU input and decremented by adding $FF (-1)._

Temporarily turning your bus into a DRAM to stuff a value into an ALU ==
living your best life

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phaedrus
This page gives the first low-level explanation I've ever found for why the
6502 requires a two-phase clock.

~~~
brian-armstrong
Yeah, pretty interesting. And I remember the TA in my digital logic lab
slapping our wrists if we tried to use latches like that.

~~~
analognoise
An FPGA is not an ASIC. Latches are totally valid design choices and they take
less silicon area if doing a custom layout. The thing is that an FPGA has a
_lot_ of time/money spent on getting the clock network and tooling for that
clock network correct in a flopped digital style, and you obviate that by
trying to force latches.

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JdeBP
The RTL Verilog that the article talks about can be found at
[http://ladybug.xs4all.nl/arlet/fpga/6502/](http://ladybug.xs4all.nl/arlet/fpga/6502/)
.

I wonder whether anyone tackled the RTL for a complete 65816 . (Daniel
Wallner's doco for T65 says that it isn't complete.)

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urmish
I had never heard of this chip. Any good resource to understand this? I am
familiar (or was at one point) with 8085/86 architecture.

~~~
0xcde4c3db
6502 and its variants were used in many platforms, particularly video game
systems and TV computers like the Apple II family, BBC Micro, Commodore
Pet/VIC-20/64, Atari 400/800, Nintendo Entertainment System/Famicom, and
TurboGrafx-16/PC-Engine. Introductory information about it tends to be
oriented toward those platforms rather than the chip itself.

[https://skilldrick.github.io/easy6502/](https://skilldrick.github.io/easy6502/)
might be a good starting point if you're already familiar with assembly
language in general (it's styled as an assembly language tutorial, but I'm not
really in a position to know how good it is at that).

~~~
urmish
Thanks. I was reading and listening to Chuck Peddle's talks last hour about
his work at Motorola and MOS. At the age of 81, he still gives talks. Very
inspiring stuff.

