Uploaded August 2016 | Updated September 2026, 2 weeks ago

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Part 2 of building the RAM module for the 8-bit computer. In this video, we add the memory address register (MAR) and DIP switches for setting the address when programming along with the logic to switch between using the register and using the switches.

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You can get all the components used in this video from any online electronic components distributor (Jameco, Digikey, Mouser, etc). See eater.net/bbcpu8-ram for more.

Complete parts list (everything in the RAM module):
- 2x 74LS189 (64-bit random access memory)
- 2x 74LS04 (Hex inverter)
- 1x 74LS173 (4-bit D-type register)
- 4x 74LS157 (Quad 2-to-1 line data selector)
- 1x 74LS245 (Octal bus transceiver)
- 1x 74LS00 (Quad NAND gate)
- 14x LEDs (9 red, 4 yellow, 1 green)
- 3x 1KΩ resistors
- 1x 0.01µF capacitor
- 22 gauge wire
- 5 volt power source (e.g., a USB phone charger)