In 1976, Motorola produced a 1-bit processor, the MC14500B. A 1-bit processor sounds like a joke, but it was an industrial controller for Boolean logic applications. I reverse-engineered the chip with die photos from @johndmcmaster via @UsagiElectric.
https://www.righto.com/2021/02/a-one-bit-processor-explained-reverse.html
In 1976, Motorola produced a 1-bit processor, the MC14500B. A 1-bit processor sounds like a joke, but it was an industrial controller for Boolean logic applications. I reverse-engineered the chip with die photos from @johndmcmaster via @UsagiElectric. https://www.righto.com/2021/02/a-one-bit-processor-explained-reverse.html
In 1976, Motorola produced a 1-bit processor, the MC14500B. A 1-bit processor sounds like a joke, but it was an industrial controller for Boolean logic applications. I reverse-engineered the chip with die photos from @johndmcmaster via @UsagiElectric. https://www.righto.com/2021/02/a-one-bit-processor-explained-reverse.html
This processor had a curious architecture: no on-board program counter or address pins. It was more of a building-block than a full microprocessor, using external chips. But not a bit-slice processor either; it was intended for 1-bit data.
The MC14500B was an early CMOS processor, for low power consumption. But it was also low-density, about 500 transistors on the chip compared to thousands for other early microprocessors. A single two-transistor inverter takes up a substantial part of the die (red box).
The MC14500B was an early CMOS processor, for low power consumption. But it was also low-density, about 500 transistors on the chip compared to thousands for other early microprocessors. A single two-transistor inverter takes up a substantial part of the die (red box).
The MC14500B was an early CMOS processor, for low power consumption. But it was also low-density, about 500 transistors on the chip compared to thousands for other early microprocessors. A single two-transistor inverter takes up a substantial part of the die (red box).
The MC14500B was an early CMOS processor, for low power consumption. But it was also low-density, about 500 transistors on the chip compared to thousands for other early microprocessors. A single two-transistor inverter takes up a substantial part of the die (red box).
The chip contains 15 flip-flops, for registers, instruction latch, and temporary storage. Each built from two 2-inverter latches, separated by transmission gates. Weak transistors in inverters let input overwrite value stored in inverter loop.
The chip contains 15 flip-flops, for registers, instruction latch, and temporary storage. Each built from two 2-inverter latches, separated by transmission gates. Weak transistors in inverters let input overwrite value stored in inverter loop.
The chip contains 15 flip-flops, for registers, instruction latch, and temporary storage. Each built from two 2-inverter latches, separated by transmission gates. Weak transistors in inverters let input overwrite value stored in inverter loop.
The chip contains 15 flip-flops, for registers, instruction latch, and temporary storage. Each built from two 2-inverter latches, separated by transmission gates. Weak transistors in inverters let input overwrite value stored in inverter loop.
The chip contains 15 flip-flops, for registers, instruction latch, and temporary storage. Each built from two 2-inverter latches, separated by transmission gates. Weak transistors in inverters let input overwrite value stored in inverter loop.
The chip doesn't support arithmetic, just seven logic operations, so it has a Logic Unit (LU) not an ALU. It's implemented with three complex gates that combine the data value (green), inverted data (orange) or RR register (blue), depending on the instruction.
The chip doesn't support arithmetic, just seven logic operations, so it has a Logic Unit (LU) not an ALU. It's implemented with three complex gates that combine the data value (green), inverted data (orange) or RR register (blue), depending on the instruction.
The chip doesn't support arithmetic, just seven logic operations, so it has a Logic Unit (LU) not an ALU. It's implemented with three complex gates that combine the data value (green), inverted data (orange) or RR register (blue), depending on the instruction.
The chip doesn't support arithmetic, just seven logic operations, so it has a Logic Unit (LU) not an ALU. It's implemented with three complex gates that combine the data value (green), inverted data (orange) or RR register (blue), depending on the instruction.
Strangely, while the chip has Jump and Return instructions, they don't do anything except activating a pin. You needed an external chip to implement jumps and a subroutine stack. Fortunately, you could buy a special-purpose stack chip.
So that's the MC14500B processor, a chip that slims down a microprocessor to the limit. With a 1-bit "word", it replaced relay-based "ladder logic" in air conditioners, motor controllers, traffic lights, etc. More details in my blog post:
https://www.righto.com/2021/02/a-one-bit-processor-explained-reverse.html
You can follow @kenshirriff.
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