cmosdigital-logicttl
From what I remember, from decades ago, 1980's 5v TTL chips would see a floating input as a zero (because they switched on current, rather than voltage). Update: it seems they were interpreted as ones.
Are there currently any families of discrete logic which interpret a floating inputs as a zero or a one, rather than a non-deterministic value? (AC, ACT, HC, HCT, ALS, AS, AC, CB, CBT, F, S, LV, LC, etc.)
The 74LCX07 will not clamp the output to \$V_{DD}\$ (the datasheet talks about \$V_{CC}\$), since its particularly targeted at interfacing between different supply voltages. Note that the inputs are 5V tolerant, also with \$V_{DD}\$ = 3.3V.
The datasheet says maximum output voltage is 5.5V (never use the 7V mentioned under Absolute Maximum Ratings), but should have mentioned for what supply voltage, for instance also for 3.3V.
The only characteristic I could find which actually indicates that a higher output voltage is allowed is off state current on page 4, which gives a value of 10\$\mu\$A at \$V_{CC}\$ = 2 to 5.5V and \$V_O\$ = 5.5V.
edit
That could have been clearer. Especially since it contradicts what it says under Absolute Maximum Ratings: "DC Output Diode Current, for \$V_O > V_{CC}\$: 50mA."
The NXP 74LVC1G07 seems to be a solution.
To level shift up from a 3.3V system to drive 5V CMOS input levels, simply connect the LVC output to a 5V termination voltage through a pullup resistor as shown below. The outputs of these devices are 5V tolerant and provide a simple solution to drive 5V CMOS input levels.
From here.
It also only mentions output clamping current for \$V_O < 0\$, so it won't clamp 5V.
First off, take that book, douse it in gasoline/petrol and burn it. Secondly, saying that something is CMOS is akin to saying that something is a circuit. There are so many variants ... Even 25 to 30 years ago CMOS ASIC flows (Gate arrays, or Sea of Gates) approaches were already way faster than any of the discrete forms of logic (AS, LS etc.). You first saw discrete logic chips that then integrated more transistors, these became known as MSI (Medium Scale integration) designs (like UARTS etc.) that may have been built on similar CMOS processes. But by the time that LSI (large scale integration) designs started to come out the processes for discrete and integrated CMOS had bifurcated and diverged. Probably at the 3 um node LSI and VLSI (Very large scale integration) design never looked back. Microprocessor processes (also CMOS) had their own design methodology and techniques.
Even at the time of publishing that book had it wrong. We were in the midst of the latest 0.13um process technology, worrying about scaling effects and yield in these new radically smaller transistors. Going from 2 um to now 20 nm (arms fully waving now) which is a factor of 100X and a scaling according to Moore's law of sqrt(2) roughly translates into 14 generations of scaling /changes.
Just to give to perspective, in 0.18 um process technology you can build a pretty sweet op-amp that has a unity gain bandwidth of about 1.2 GHz (0.8 ns) which is good for 14 bits SNR. This is CMOS technology that dates back to the late 1990's.
If I recall correctly, you could build 2 GHz logic designs in 0.13um processes with full clock trees and fan out quite nicely.
Best Answer
Unused TTL inputs are high = 1; Fairchild's application note 363: Designing with TLL says:
While not all TTL-like families based on BJTs ((A)LS, (A)S, F, etc.) use the emitter of a BJT as input, they are designed to behave the same way.
CMOS devices use MOSFET gates as inputs. This implies that floating inputs can lead to an half-on state where the input state is indeterminate, or oscillates (see, for example, TI's application note Implications of Slow or Floating CMOS Inputs).
The only practical way of giving a CMOS input a 'default' value is to use a pull-up or -down resistor, but it's usually not done for discrete logic because it would reduce the input impedance by a great amount.
(Some CMOS devices have bus-hold circuits to prevent their inputs from floating, but the power-up state still is undefined.)