Any other SX28 users out there?

[Analog Kid]

Probly about a decade ago or so I built a couple of projects based on the SX28 micro, which at that time was sold by Parallax. (I believe, but am not sure, that this chip is now sold by Microchips?)

I really liked using this li'l uP. Just the right amount of support on-chip: RTCC, sufficient ports, interrupts, all that. An easy-to-use assembly language.

I still have some chips, but no programmer: I borrowed the programmer from a friend (ex-boss) who needed it back. At that point it was RS232 based, not USB.

Is there a USB-based programmer for this chip? Is it still supported? I can see some future uses for this guy ...

[aeg]

Not now sold by anyone. Microchip sued Scenix for patent violation, no further parts were made, Parallax bought the remaining inventory and sold them until they ran out. Accordingly, not suitable for new designs.

[Analog Kid]

Scenix, that's right. Pity; it really is a very nice little machine.

So what would you say is the closest thing to this chip currently available? ATtiny? something else?
My preferences: the ability to program the chip in its native (assembly) language, not C or C++. And simple support not requiring a complex IDE.

[westfw]

It's not clear how much the lawsuit had with the demise of the chips, IMO.

It's just that chips "fast enough to bit-bang all your peripherals" became sort-of uninteresting in the era of chips that ran equally fast AND had peripherals.  Ubicom (which is what Scenix morphed into) tried to focus on wireless networking, but so was everyone else.  Eventually they were absorbed by Qualcom (rather after the SX chips were gone, I think.)

what would you say is the closest thing to this chip currently available? ATtiny? something else?

An ATtiny (or any AVR) is nicely programmable in assembly language, as are the MSP430 series from TI.

Some of the ARM Cortex chips might be closer to matching the SX instruction rate (50MIPs, in the original version.)  The Raspberry Pi RP2040 (Pico) and RP2350 (Pico2) in particular have their "PIO State Machines" that give you some of the advanced bit-banging capabilities.  But the ARM is not particularly friendly for ASM programming.

[Andy Chee]

Instruction set wise, the Ubicom/Scenix/Parallax SX line of chips more closely resembles the 8-bit PIC 16F series.

However whilst the SX is capable of 75MIPS, the 16F maxes out at 10MIPS.

The SX speed advantage is tempered somewhat by the number of peripherals available on the PIC, so you don't have to bit-bang these peripherals as you would on the SX, thus a slower 16F can still manage with its peripherals.

Today, there are faster PICs than the 16F series that have C-optimised instruction sets making them more friendly to code, for example, the 18F series.  It's a bigger instruction set, but not onerous.  So can still be coded in assembly if desired.

There is no USB programmer for the SX per se.  Parallax just tacked on an FTDI232 to their existing serial programmer.

[oPossum]

So what would you say is the closest thing to this chip currently available?

https://www.parallax.com/propeller-1/

[Andy Chee]

Propeller is a completely different architecture to the SX.  I wouldn't call them close at all.

[oPossum]

Peripheral functions implemented mostly in software. Similar in concept.

[macboy]

...
I really liked using this li'l uP. Just the right amount of support on-chip: RTCC, sufficient ports, interrupts, all that. An easy-to-use assembly language.

RTCC? They had timers (their only real peripheral) but not RTCC that I recall, but I'm probably wrong because I never had use for an RTCC. I'm more familiar with the SX48. The interrupt handling was so good. It has a hardware stack which saved all the important context registers so the ISR could get straight to businesses without needing any save/ restore steps. The ISR could run and be done in well under a microsecond. I'd like to see a modern micro pull off that trick, with their ISRs written in C.

The GPIO were also amazing. All ports individually configurable as TTL, CMOS, or Schmitt trigger input type.

Is there a USB-based programmer for this chip? Is it still supported? I can see some future uses for this guy ...

Yes they made a usb programmer. Supported? No. The chips themselves have been out of production for about a decade and umobtainium for at least five years. The SX48 was originally at least $10 a pop, but at the end parallax was selling the last of the stock for pennies (I remember seeing 35 cents or so each). The tools disappeared even longer ago. I bought an SX-KEY USB programmer in 2011, and it was end of life status then.  The very simple IDE does run fine on 64 bit windows, so if you can get your hands on an SX-KEY, you should be able to use it, if that is what you mean by supported.

[Andy Chee]

RTCC? They had timers (their only real peripheral) but not RTCC that I recall, but I'm probably wrong because I never had use for an RTCC. I'm more familiar with the SX48.

All members of the SX family had an 8-bit RTCC (equivalent of Microchip PIC’s TMR0).

But the SX48/52 had extra 16-bit timers which were advantageous for generating high resolution PWM.

The SX also had a single analog comparator, which one could feedback the PWM, and turn it into a successive approximation ADC.