I'm building a breadboard 8-bit computer (Ben Eater design: https://eater.net/). However, I decided to substitute two 74ls173 (D flip-flops) with one 74hct377. The register works as expected, but the 74ls245 doesn't output the data to the bus. What did I check:

  1. The connections seem ok. The Buffer is working in A->B direction (pin 1 high). The output is enabled (pin 19 is low). Both ground and VC are connected.
  2. The buffer receives data on pins A. The voltage is approx. 2,5V.
  3. The supply voltage is a bit too low: 3,5-4V. My power supply is supposed to give 5V, but I got Voltage drops (I have difficulties handling them). Anyway, other IC seem to work well enough on 3,5-4V, even the 74ls245 at the other location in the circuit.

Here goes the photo of my ciruit. Any ideas how to solve this? Maybe some other IC for buffer that handle lower power supply? enter image description here


Fix your power distribution! Use individual power and ground wires from the power supply to EACH breadboard - do not daisy-chain the power distribution through multiple breadboards.

The 74LS family is specified for operation between 4.75 and 5.25 volts - you can't expect proper operation at 3.5 volts. The CMOS versions (74HC, but not 74HCT) are specified for operation from 2 - 6 volts. 74HCT is spec'd for 4.5 - 5.5 volts.

  • \$\begingroup\$ Also the LS245 is very power hungry - up to 95mA quiescent current draw! Best to avoid it if possible... \$\endgroup\$ – Bruce Abbott Aug 26 '17 at 19:14

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