Testing our computer's registers - 8-bit register - Part 5
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange users cite it when they are debugging or understanding the same 74LS173 and 74LS245 register circuit on a breadboard, including LED loading and logic-level problems.
Recommended by 0 people across 0 different months, 2017 to 2023.
What it is
Part 5 of Ben Eater's breadboard 8-bit computer series. He tests the 8-bit register built in the previous video and wires up two more identical registers, giving an A register, a B register and an instruction register, built from 74LS173 registers, 74LS245 bus transceivers and LEDs.
What people said
Cites Karol Pogorzelski · 2017-03 · Electrical Engineering Stack Exchange · on “Problem with testing 74ls173AN D flip-flop”
I'm building a simple 4-bit computer (a Nibbler) from 74 series ICs on a breadboard. Right now I'm working on 74LS173AN IC registers. I can't make it work. I have connected the input enable (pin 9,10), output control (1,2), and clear (15) to ground and some data inputs to vcc. The output pins (Q1-Q4) are connected to ground via LEDs. I'm simulating the clock signal by swithing a tact-switch on/off (with ground connected by 10k resistor and direct connection to VCC. I tried different connections and searched web (many hopes with [this video] , but it didn't help). Nothing works. I suspect there might be a problem with clock signal, but I would really appreciate the opinion from an experienced elec
Cites Mason Ticehurst · 2019-09 · Electrical Engineering Stack Exchange · on “Passing <5V through bus of tri-state transceiver”
I am following a schematic which implements a basic 8-bit register. The schematic is pictured below: [LINK] According to the datasheet [LINK] of the 74LS173 chip, The high-level output voltage is 2.4V with testing conditions assuming the minimum input voltage (although my case V cc is 5V). The current configuration is set to output ~2.4V at each output pin on the 74LS173. I can confirm that the output is indeed ~2.4V. It appears that this chip is functioning perfectly well. The chip receiving this 2.4V potential is the SN74HC245. This chip is also fed 5V V cc . The datasheet only states two input states (high + low) high being >3.15V at 4.5V V cc and low being <1.35V at 4.5V V cc . It is wir
Cites Greenonline · 2023-02 · Electrical Engineering Stack Exchange · on “How does putting an LED in parallel with an 8-bit computer load affect the voltage/current of a circuit?”
The highest voted comment [this video] , from Jason Smith, under the video points out this issue: NOTE! Watch your forward voltage drop on your LEDS(they act like a voltage divider*). I needed to add resistors to keep the logic voltage high enough for the ls245 to recognize. A small bald spot ensued trying to debug :) along with the follow up comment: Your LED should drop approx 1.7 volts from your logic level, putting it below 2.0(logic high,ttl). Put a 1k resistor in series to limit current and keep your voltage up. ttl output - resistor - led. Test all 3 points with a voltmeter and you will see better.