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In case you’re a bibliophile, going to a used bookstore is a distinctly satisfying expertise. Certain, you may uncover an outdated e-book you wish to learn. However no less than a part of the endorphin rush comes from seeing outdated buddies. 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 Nevertheless it’s a cheerful feeling to see an outdated pal and possibly flip by means of them studying a passage or two between cabinets of musty books.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 solution 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 number 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”. Effectively, naturally, somebody wanted some for some motive, so I needed to dig every part up. Understanding that these could possibly be among the final unscheduled SX chips on the earth made me really feel a bit nostalgic.

The historical past

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

After all, many firms 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. Specifically, whereas it may assist comparatively excessive clock charges (20 MHz was widespread), every regular instruction took 4 clock cycles. So when his crystal stated 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 would take binary code meant for a PIC and implement it on the SX. So the system had the identical architectural quirks because the PIC, which was each a plus and a minus. Nonetheless, it had one massive benefit over the PIC: it may run at true 50 MHz. The SX used a pipelined structure, so it was capable of 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 plenty of energy, but it surely could possibly be adjusted by decreasing the frequency. Even at 10 MHz, it ran twice as quick as a PIC. Later variations may run at 75 MHz and even 100 MHz, although these have been shortly discontinued. Nonetheless, these chips have been routinely overclocked to no less than 80 MHz on, say, XGameStation.

The SX-Key offered programming and debugging on the SX clock pins.

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

Peripherals Just about

A key idea of the SX was that the CPU was stored quite simple to maintain prices down and improve velocity. The pattern, in fact, was so as to add issues to CPUs like UARTs, timers, PWM turbines, and the like. The SX did it otherwise. Operating quick and having a really deterministic method of dealing with interrupts, Scenix touted a library of “digital peripherals”. The thought was that through the use of interrupts, you would 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 may adapt all of the belongings you need. Do you want three UARTs and a PWM channel? No drawback. In case your subsequent venture wants 5 PWM channels and no UARTs, you are able to do that too. After all, this was at all times higher in principle than in observe. The “library” was little greater than pattern code, and generally integrating it into your code was a problem. This was very true if you happen to have been making an attempt to combine multiple, as they often had conflicting necessities.

Nonetheless, it may do fairly a number of issues that might have been practically 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 recognized 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 have been just about direct replacements for his or her present merchandise however a lot sooner. (And, in fact, extra vitality). Additionally they provided the programming chips and {hardware} they designed at inexpensive costs, making the SX considerably standard with the hobbyist neighborhood.

A Parallax improvement board with the SX-Key plugged in.

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 widespread operations like FSK, I2C, SPI, run LCDs and stepper motors, and way more.

For 2005, Ubicom would transfer away from the SX and promote them solely to Parallax underneath the Parallax model. In mid-2009, Parallax introduced the tip of the street for the SX. Nowadays, you may select a 32-bit processor that may run at 100MHz for a track, and built-in debugging is widespread. Fashionable CPUs may have architectures which can be a bit extra smart than the outdated PIC financial institution switching scheme and in addition 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 pal the SX.

What outdated processors are your mates? I actually just like the RCA 1802. I’ve additionally executed plenty of work on older Motorola gadgets just like the 6805 and 68HC11. I additionally loved the fundamental seal. I am unable to assist however surprise if, in 30 years, folks will fondly bear in mind an STM32 system or maybe the Raspberry Pi Pico.

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Chips Remembered: The Scenix/Ubicom/Parallax SX

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