Migrating... 6502 to 65816 to ... ?

[BigEd]

(Interesting - a 68k with a reasonable amount of RAM included. But £25 to £30 - not super expensive as you say, but also not super cheap.)

[AndrewP]

AndrewP wrote:

jds wrote:

68000 is another option worth considering. There's a lot more software available and you can still get microprocessors. People are building their own 68030 designs without much trouble, and there is a lot of capability there. Plus it's easy to interface with the same I/O chips we are already using.

I've thoroughly thrown in with the 65816 but in my exploration of the intertubes I've stumbled across the Coldfire a couple times. And if I ever move on from the '816 that's probably where I'd go.

Specifically the NXP ColdFire V2 in the TQFP package (MCF5249LAG120).

It's a 68000 compatible CPU which can interface with SRAM (although those pins can be programmed to interface with SDRAM instead). I don't know the 68000s well enough to spot the differences with the ColdFire V2 core but it basically looks like a bunch of peripheral modules and and address decode strapped around it. And 128KB of in-chip SRAM.

It's also not in a crazy BGA package and still appears to be available in the 10s of thousands and isn't *that* expensive.

BigEd wrote:

(Interesting - a 68k with a reasonable amount of RAM included. But £25 to £30 - not super expensive as you say, but also not super cheap.)

Yup, as a poor South African $30 is a quite a lot of money - a decent meal for 4 people. But as a crazy bastard running three '816s in parallel to get a fraction of the performance... well after adding in UARTs, RAM, ROM and glue logic I'm already way over $30. I don't think I'm the normal use case though . The ColdFire competing with something like the Raspberry Pi Pico... there's just no comparison.

[barnacle]

Thinks... has the pico enough io pins to pretend to be a 6507, I wonder?

Neil

[drogon]

barnacle wrote:

Thinks... has the pico enough io pins to pretend to be a 6507, I wonder?

Going by the various Pico6502 projects out there, then almost certainly.

But you can still buy 6507's - and there is currently one "for sale" 6507 kit out there and very soon (probably) a 2nd (mine) too.

Then you can experience the glory of waiting 58 seconds per generation of Life on a 23x38 board...

Back to Coldfire/68000 ... I did look at them when looking to move my project onto the next thing but (probably irrationally) the thing that put me off was that it was Big Endian.

So I stuck with ARM.

-Gordon

[AndrewP]

barnacle wrote:

Thinks... has the pico enough io pins to pretend to be a 6507, I wonder?

barnacle wrote:

Going by the various Pico6502 projects out there, then almost certainly.

Absolutely it could masquerade as a 6507, it has 26 GPIOs on the standard Raspberry Pi Foundation board.

I think it could become a full drop in 6502 also (possibly not a 65C02). The pins that have to be present are:
A0..A15
D0..D7
PHI0 IN
RWB
-----
26

Almost certainly necessary:
IRQB
NMIB
RDY
SYNC
-----
4

Gonna have to roll without:
PHI1 OUT
PHI2 OUT
S.O

Now 26 + 4 pins is more than the 26 GPIOs that the standard Pico board has. But it's relatively easy to break out some of the onboard IOs (the LED and voltage sensors specifically) to get to 28 GPIOs. And then it's possible but harder to break out another two of the onboard GPIOs for 30 in total. Easier to just buy an RP2040 board that already has them present though.

PHI1 and PHI2 are easier enough to generate with 74 ICs (does RDY affect them?) and hopefully no one ever uses S.O.

You've probably noticed the absence of RESB but it should map directly to the Pico's RUN pin.

A couple of caveats: the Pico doesn't drive very hard so you'd have to buffer the outputs with HCT ICs (or similar) and the bi-directional lines with a TXS0108 or LSF0108. The upside is that that converts the 3.3V Pico to a 5V device (note: the Pico is NOT 5V tolerant).