Ben Eater's Homebuilt Computer

[Bob Kuczewski]

In this video, Ben adds the additional gates needed to expand the SR Latch into a "D" latch. The "D" Latch stores a data bit (D) whenever the enable signal is active.

https://www.youtube.com/watch?v=peCh_859q7Q

[Bob Kuczewski]

In this video, Ben shows how to add edge triggering mechanisms to convert a "D Latch" into a "D Flip-Flop". For simplicity, Ben chooses to use a simple "RC" (Resistor/Capacitor) circuit to create the edge trigger for his "D Flip-Flop".

https://www.youtube.com/watch?v=YW-_GkUguMM

[Bob Kuczewski]

Clock

In this video, Ben describes how to use the 555 timer chip in astable mode to make a variable speed clock. Ben discusses a number of electrical considerations needed to keep the clock within the desired specifications.

https://www.youtube.com/watch?v=kRlSFm519Bo

[Bob Kuczewski]

Clock

In this video Ben uses a second 555 timer in monostable mode to eventually add a single step button to the clock. The monostable mode is used for "debouncing" the switch to ensure that there is only one clock pulse per button press.

https://www.youtube.com/watch?v=81BgFhm2vz8

[Bob Kuczewski]

Clock

In this video, Ben adds a selector switch to operate the clock in either free-running mode or single-step mode. Again, the switch will need to be debounced and Ben uses another 555 timer (mostly as an SR latch).

https://www.youtube.com/watch?v=WCwJNnx36Rk

[Bob Kuczewski]

Clock

In this video, Ben finishes the Clock module which includes the following features:

- Adjustable clock frequency
- Ability to enable/disable the clock manually
- Ability to enable/disable the clock programatically
- Ability to single step the clock

https://www.youtube.com/watch?v=SmQ5K7UQPMM

[Bob Kuczewski]

Registers

In this video Ben begins building registers that will store values and be visible from the central 8-bit bus. Ben uses a Tri-State buffer (74LS245) for each register so that multiple registers can be physically connected to the same bus without voltage contention (short circuits). Ben describes the functionality of the bus as a communication pathway between the different modules in the computer.

https://www.youtube.com/watch?v=QzWW-CBugZo

[Bob Kuczewski]

Registers

In this video Ben describes the 74LS245 Tri-State buffer and explains why they are needed to interface modules to the shared bus.

https://www.youtube.com/watch?v=faAjse109Q8

[Bob Kuczewski]

Registers

In this video, Ben builds a 1-bit register to show how it could be done with simple logic gates and a D flip flop. Ben also discusses the 74LS245 which will be used to interface to the bus.

https://www.youtube.com/watch?v=-arYx_oVIj8

[Bob Kuczewski]

Registers

In this video Ben describes how he will use the 74LS173 4-bit registers to store data, but isolate them from the bus with a 74LS245 Tri-State buffer. This has the advantage of making the current register values available for display even when the register is not output to the bus.

https://www.youtube.com/watch?v=CiMaWbz_6E8