#electronics # 74LS189 Replacement [Replacing 74LS189 with 6116P – StrayPaper](http://blog.straypaper.com/2017/12/02/replacing-74ls189-with-6116p) # 74LS vs HC * [integrated circuit - 74LS vs. 74HC series ICs for Ben Eater's 8-bit Computer - Electrical Engineering Stack Exchange](https://electronics.stackexchange.com/questions/358620/74ls-vs-74hc-series-ics-for-ben-eaters-8-bit-computer?rq=1) ## Input Voltage The input voltage for the LS and HC series is close, but the HCT series mimics the LS series in terms of a '1' input and a '0' input. 74HC needs more voltage to be considered a logic '1'. Both types have a no-mans land of about 2.5 VDC where it is in a linear mode and may oscillate. ## Input Impedance The 74HC series has a very much higher input impedance than the 74LS, which actually 'leaks' a small positive current out of an input pin. It is in the uA range so normally is not an issue. ## Output Drive Current The 74HC series has an output drive current of +/- 25 mA, so with a resistor it can drive LED's directly. A 330 ohm to 1 K resistor will cover most LED's except the "high-powered' types. The 74LS can sink a couple of mA and source about 1 mA at most. ## Output Drive Voltage The 74HC outputs swing rail to rail, even with a 15 mA load to either rail. The 74LS series can sink an output close to ground voltage, but can only source Vcc-1.2 volts due to its bjt outputs. It is very common to see pullup resistors on both the 74HC and 74LS data and address lines to prevent floating if nothing is driving the bus, but the 74LS series used them to help make logic '1's closer to the Vcc supply rail. ## Current Consumption The 74HC/74HCT series also consumes MUCH less current, just a few uA in a static mode. The 74LS consumes 1,000 times as much idle current.