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By Brian Benchoff
John has an interesting, if old piece of tech sitting on his workbench. It’s an Ohio Scientific C3-8P computer from the late 70's by way of a few garages, basements, and attics. As with most tech of this vintage, there are some problems, and John found debugging a little frustrating without the ability to trace and watch the programs. He needed a logic analyzer, and found one in an unlikely piece of hardware.
John built one using a Teensy micro-controller, and further refinement of this project could turn it into a full in-system emulator.
The old Ohio Scientific computer John is trying to bring back from the dead is based on the 6502 CPU. That’s sixteen address lines to monitor, eight data lines, and four control lines. These were wired directly to a Teensy 3.1.
Reading and controlling all the signals from a 6502 is a task that falls to Linux. A command line program controls the Teensy and is capable of reading memory, setting trigger addresses, dumping the entire address space to a file, or just recording the last 5,000 clock cycles. This kind of tech existed back in the late 70's and early 80's. It also cost a fortune. Now, with a $20 Teensy and probably another $30 in ribbon cables and test clips, anyone can build a logic analyzer for a very old computer system.
Videos below.
John has an interesting, if old piece of tech sitting on his workbench. It’s an Ohio Scientific C3-8P computer from the late 70's by way of a few garages, basements, and attics. As with most tech of this vintage, there are some problems, and John found debugging a little frustrating without the ability to trace and watch the programs. He needed a logic analyzer, and found one in an unlikely piece of hardware.
John built one using a Teensy micro-controller, and further refinement of this project could turn it into a full in-system emulator.
The old Ohio Scientific computer John is trying to bring back from the dead is based on the 6502 CPU. That’s sixteen address lines to monitor, eight data lines, and four control lines. These were wired directly to a Teensy 3.1.
Reading and controlling all the signals from a 6502 is a task that falls to Linux. A command line program controls the Teensy and is capable of reading memory, setting trigger addresses, dumping the entire address space to a file, or just recording the last 5,000 clock cycles. This kind of tech existed back in the late 70's and early 80's. It also cost a fortune. Now, with a $20 Teensy and probably another $30 in ribbon cables and test clips, anyone can build a logic analyzer for a very old computer system.
Videos below.