Chips Remembered: The Scenix/Ubicom/Parallax SX

In the event you’re a bibliophile, going to a used bookstore is a distinctly satisfying expertise. Certain, you would possibly uncover an outdated e book you need to learn. However no less than a part of the endorphin rush comes from seeing outdated associates. Not people, however books you learn years and even a long time in the past. More often than not, you do not purchase the e book; you most likely have one hidden in a field someplace. Nevertheless it’s a cheerful feeling to see an outdated good friend and perhaps flip by means of them studying a passage or two between cabinets of musty books. I want we had one thing like that for fries. Exterior of some notable exceptions, chips are inclined to have a brief lifespan of recognition after which give option to different chips. That is very true of CPUs. One I particularly miss is the Scenix/Ubicom/Parallax SX chip.

The opposite day I had a bookstore-like expertise with this processor. I produced a couple of merchandise primarily based on these chips and have a small stash of them left. I jealously guard the required {hardware} to program them “simply in case”. Nicely, naturally, somebody wanted some for some motive, so I needed to dig every part up. Realizing that these might be among the final unscheduled SX chips on the planet made me really feel a bit nostalgic.

The historical past

Within the late Nineteen Nineties, an organization referred to as Scenix started producing a microcontroller referred to as the SX in a couple of footprint sizes. So the SX18 was, for instance, an 18-pin half. By 1999 they had been already in full swing with the SX18 and SX28 and launched the SX52.

After all, many corporations produced microcontrollers. The Scenix provide was a bit particular. In these days, the Microchip PIC was king of the hill. The PIC is an odd beast that advanced from a really restricted controller made to be small and cheap. Particularly, whereas it might help comparatively excessive clock charges (20 MHz was frequent), every regular instruction took 4 clock cycles. So when his crystal mentioned 20 MHz, it was executing directions at 5 MHz.

The SX duplicated the Microchip directions, however not the opcode mnemonics, since that was legally encumbered. In principle you might take binary code supposed for a PIC and implement it on the SX. So the gadget had the identical architectural quirks because the PIC, which was each a plus and a minus. Nevertheless, it had one huge benefit over the PIC: it might run at true 50 MHz. The SX used a pipelined structure, so it was in a position to execute one instruction per clock as soon as the pipeline was full (and assuming you did not invalidate the pipeline with a bounce).

That was 10 instances the precise velocity of a PIC. After all, at 50 MHz, the chip consumed a whole lot of energy, however it might be adjusted by reducing the frequency. Even at 10 MHz, it ran twice as quick as a PIC. Later variations might run at 75 MHz and even 100 MHz, although these had been rapidly discontinued. Nevertheless, these chips had been routinely overclocked to no less than 80 MHz on, say, XGameStation.

There was one other cool characteristic that appears regular in the present day, however was a revolution on the time: low-cost in-circuit debugging. Most older CPUs needed to have an costly particular half to do reside debugging with out further on-chip software program. Certain, you might write a debugger that may speak to a serial terminal, however that assumes a whole lot of issues are already working. Doing actual debugging on the {hardware} degree was often very costly. However the SX had all the required {hardware} on each chip. A small serial port dongle was out there that did not price a lot and with it, you might debug the chip in your circuit with no actual influence in your code.

Peripherals Nearly

A key idea of the SX was that the CPU was stored quite simple to maintain prices down and improve velocity. The development, after all, was so as to add issues to CPUs like UARTs, timers, PWM mills, and the like. The SX did it otherwise. Operating quick and having a really deterministic approach of dealing with interrupts, Scenix touted a library of “digital peripherals”. The thought was that through the use of interrupts, you might create software program peripherals and even when they consumed, say, half your CPU time, it might nonetheless run a lot sooner than a PIC with peripherals.

After all, if that works, that is nice as a result of you’ll be able to adapt all of the belongings you need. Do you want three UARTs and a PWM channel? No downside. In case your subsequent mission wants 5 PWM channels and no UARTs, you are able to do that too. After all, this was all the time higher in principle than in observe. The “library” was little greater than pattern code, and typically integrating it into your code was a problem. This was very true in case you had been attempting to combine a couple of, as they generally had conflicting necessities.

Nonetheless, it might do fairly a couple of issues that may have been almost inconceivable to do in software program on a slower CPU.

The parallax connection

Scenix ultimately grew to become Ubicom, which might ultimately turn into Qualcomm, however these chips are additionally related to Parallax, an organization identified for its core stamps, as soon as the gateway to microcontrollers. Their merchandise used Microchip’s PIC they usually started promoting a line of SX-based stamps that had been just about direct replacements for his or her current merchandise however a lot sooner. (And, after all, extra vitality). Additionally they provided the programming chips and {hardware} they designed at inexpensive costs, making the SX considerably well-liked with the hobbyist group.

Parallax additionally developed books and programs for the chip. (I even wrote a few of them). A library existed that had code to do many frequent operations like FSK, I2C, SPI, run LCDs and stepper motors, and rather more.

For 2005, Ubicom would transfer away from the SX and promote them solely to Parallax below the Parallax model. In mid-2009, Parallax introduced the top of the street for the SX. Nowadays, you’ll be able to select a 32-bit processor that may run at 100MHz for a tune, and built-in debugging is frequent. Fashionable CPUs can have architectures which can be a bit extra wise than the outdated PIC financial institution switching scheme and likewise extra appropriate for C compilers. So I do not miss these outdated days. However like an outdated e book in a bookstore, it is good to see my outdated good friend the SX.

What outdated processors are your pals? I actually just like the RCA 1802. I’ve additionally executed a whole lot of work on older Motorola units just like the 6805 and 68HC11. I additionally loved the essential seal. I can not assist however marvel if, in 30 years, individuals will fondly bear in mind an STM32 gadget or maybe the Raspberry Pi Pico.