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The Alto was a revolutionary computer designed at Xerox PARC in 1973 to investigate personal computing. The Xerox Alto is behind the oscilloscope. In the photo above, the bottom oscilloscope trace shows several sectors as they are read from disk. The oscilloscope shows the sector pulses (top, blue), clock (middle, green), and data (bottom, yellow). The PWM latch (Pulse Width Modulation) combines the oscillator signal and the feedback to generate pulses of the right duration. 4. The typical quartz oscillator is built using a simple circuit called the Pierce-gate oscillator, where the crystal forms a feedback loop with an inverter. Stability is an issue in all amplifiers with feedback, whether that feedback is added intentionally or results unintentionally. I looked around on the issues that were reported for this camera board, and thats when I stumbled upon an issue complaining about horizontal banding: IMX585 Power - Horizontal banding and 3.3V power rail noise. The handset shown above is an H-350 noise cancelling type actually designed for the new digital field telephones. The shoulder straps lacked simple D rings above the adjusters to enable you to hang the handset near your ear.

The FPGA chip contain numerous logic blocks along with a switch matrix that allows them to be interconnected as desired. But, a logic probe on the switch row connector (CN11) should show the matrix being scanned. The connector type used is the UHF SO-239 female connector. If you're not familiar with a FPGA (field-programmable gate array), it is a chip that can be programmed to generate custom hardware. The idea is we can hook this up to the Diablo drive to read and archive disks. Last week, I discovered that our boot disk had been overwritten with random data decades ago to test the drive (details). Some people were concerned, though, that the disks could get damaged in a boot attempt, losing their historical data. Though it has low current, the pull-up or pull-down resistor provides the connected voltage to the lead; when the opposite voltage connects directly without resistance to the lead, the lead takes on the unresisted voltage (imagine a voltage divider where one resistor is a switch instead of a resistor); the resistor insures that the two supplied voltages do not get directly connected (which would turn the IC off). Unfortunately we didn't get the disk in time for today's session, but we'll try it out next session.

I borrowed a couple of them and we'll try reading them later. Each "row" must contain the same number of "column"s; use null to fill in blank spaces, but try to minimize them. The transformer must also suppress anyresponse to the common-mode voltage. It must have adequate gain to boost the input voltage to a level that is sufficient to drive a power low-noise amplifier. The result of doing this, called dynamic CMOS, is a circuit whose output can drive regular CMOS circuitry, but not another dynamic CMOS circuit; the addition of a CMOS inverter on the output, as shown, leads to domino logic. Then we can connect the Emulator to the Alto and simulate multiple disk packs without physically handling disks. But then terminology shifted, with "Colpitts oscillator" and "Pierce oscillator" indicating two different types of crystal oscillator: Colpitts with the capacitors and Pierce without the capacitors. In 1923, George Washington Pierce, a professor of physics at Harvard, replaced the inductor in the Colpitts oscillator with a crystal. Getting back to the oscillator module I examined, it could be described as a common-drain Colpitts oscillator (analogous to common-collector). The key feature of the Colpitts oscillator is the two capacitors, which form a voltage divider.

Since the capacitors are grounded in the middle, the two ends will have opposite voltages: when one end goes up, the other goes down. It's also called a single-pin crystal oscillator since only one pin of the crystal is connected to the circuitry (and the other is grounded). The point of this history is that oscillator terminology is confusing, with different sources calling oscillators Colpitts or Pierce in contradictory ways. Colpitts oscillators are explained in videos at Hackaday. 6. If you want to learn more about quartz oscillators, there are interesting videos at EEVblog, electronupdate, and WizardTim. I'm not sure why the module I disassembled uses a more complex oscillator circuit that requires tricky biasing. Historically, it would be called a Pierce oscillator since it uses a crystal. The Pierce oscillator circuit commonly used as a computer clock. Y Combinator received an Alto from computer visionary Alan Kay and I'm helping restore the system, along with Marc Verdiell, Luca Severini, Ron Crane, Carl Claunch and Ed Thelen. Instead, Josh Dersch at the Living Computer Museum in Seattle is sending us a fresh boot disk with no historical significance.