Fascinating Look at a Gas Station Pump Computer from 1993

A gas station pump laptop sits quietly hidden away in a metallic cupboard, processing transactions day after day, as most automobiles go proper by with no second thought. Dave from Usagi Electrical found considered one of these often-forgotten machines at a swap market and reworked it right into a loopy journey of reverse engineering. The tip product is a take a look at 80s industrial know-how that also works many years later.

This technique was launched round 1993, nonetheless its origins may be traced again to the Eighties. Gilbarco most definitely designed it as a forecourt controller, which is the mind that coordinates all the fuel pumps and point-of-sale techniques of a fuel station. Fairly than having a single chip inside every pump, the whole system is structured round a modular rack of circuit boards which might be all related through a VME backplane. It has six slots for added parts, and the ability rails are designed to offer regular voltages even after years of use.

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The Motorola MC68HC000FN processor serves because the mind of the operation. This 16/32-bit processor is much extra highly effective than is required for easy pump logic, however it was a powerhouse again then. There are additionally various help chips round it, reminiscent of a parallel interface timer, a Zilog twin serial communications controller, and a real-time clock chip that retains monitor of the date, time, and even leap years. There are oscillators holding every thing operating on the right frequencies, one at 10 MHz for the CPU and one other at round 4.9 MHz for serial communications.

The reminiscence is housed on a separate card, which has three 27C210 EPROMs that retailer the firmware and complete 384 KB. That was a whole lot of working RAM for an embedded controller again then. There are a couple of programmable logic units and bus transceivers that join every thing collectively. Nonetheless, one of many capacitors on this board is getting previous, and there’s a risk that it’ll start to leak over time, an previous electronics drawback that’s all too prevalent.

There are two further serial playing cards stuffed in there to develop the connectivity, every carrying two Z85C3010 chips, providing you with 4 serial ports per card for a complete of eight, however while you’re truly operating the comms, it’s over RS-485 twisted pair, a alternative constructed for noise resistance throughout lengthy distances. The jumpers on the playing cards permit you to configure numerous choices, however you’ll need to dive deep to determine what they’re purported to do. The ability provide is a switch-mode unit from the early Eighties that gives +5V at 6A, +12V at 2.5A, and numerous smaller rails for remoted circuitry. There are giant capacitors smoothing out the output, and even after years of storage, it nonetheless produces clear voltages.

Firmware lies in these EPROMs that run pSOS, a really previous Actual-time working system from the Eighties. The moniker “Moveable Software program On Silicon” remained as a result of it match so properly on embedded processors just like the 68000 household. This small working system is all about getting the timing right for duties like pump authorization, gas move monitoring, transaction logging, and communication with fee terminals in addition to central station techniques.

When Dave initially turned on the board stack, the LEDs flashed and one of many RS-485 ports despatched out a repeated sign. Hooking it as much as an oscilloscope revealed that the info pulses have been coming in at roughly 4800 baud, however they have been all in a bespoke bit format reasonably than normal ASCII. Tying in a terminal to have a look yielded nothing coherent. That is sensible, on condition that the machine was designed to speak with different industrial tools reasonably than people. After experimenting with the byte order for the big-endian structure, a couple of extracted strings from the ROMs often yielded acquainted phrases reminiscent of “deal with,” “alarms,” and “allowed,” referring to a few of the previous menu-driven or status-reporting functionalities it used to have.
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