If you use the spreadsheet’s IF statement, the IF reads: So, the formula to put into cell C1 is A1 x B1. In this case, it says, “if A1=0, then make this cell equal to 1, otherwise make it 0.” For obvious reasons, I prefer to use the “one minus” approach.įigure 2 shows some other simple gates, but let’s do them one at a time.įor the AND gate at the top left corner of Figure 2, the truth table (which describes how it works) is shown in Table 1, from which we can see that the output is just the product of the two inputs: a simple multiplication. The parentheses contain three arguments: a test what to do if the test is correct and what to do if it isn’t. Another way is to use the spreadsheet’s IF function, like this: Make sure to check the exact format for whichever spreadsheet you are using. In Excel, you’d type =1-A1 into cell B1 (with the equal sign) whereas, in most other spreadsheets, it would be just 1-A1. In other words, in the spreadsheet, cell B1 should be equal to one minus whatever is in cell A1: 1 minus 0 is 1, whereas 1 minus 1 is 0. The simplest is to write this as the simple formula: Now all you have to do is put the right formula into cell B1, so it’s always the opposite of A1, and you’re done.įor the inverter in Figure 1, if the input is a 0, then the output is a 1, and if the input is 1, then the output is 0 (you have to use 0 and 1, because it won’t work if you try to use H and L or True and False instead). There’s nothing magic about these two cells, as you could use any two cells in the spreadsheet. Simply label them A1 and B1, and right away, you get the idea: Just use cell A1 in the spreadsheet for the input and cell B1 for the output.
Looking at an inverter - such as a 7404 - in the TTL manual, you’ll often see the inputs and outputs labelled as In and Out, or perhaps A and B. The Inverterįigure 1 shows the basic idea.
For the examples that follow, I'll use Excel. It doesn’t have to be an expensive or powerful spreadsheet program. Here's an interesting and simple technique for simulating these circuits on a computer using a spreadsheet program. Short of actually building these (and other digital) circuits, it’s sometimes hard to check that they do what they claim to do. I recently read two articles about linear-feedback shift registers, which are shift registers with some of their outputs fed back to the input for generating cyclic redundancy check (CRC) bits or random numbers.
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