Editing Transistor–transistor logic (section)

==Applications==
Before the advent of [[Very-large-scale integration|VLSI]] devices, TTL integrated circuits were a standard method of construction for the processors of [[minicomputer]] and midrange [[mainframe computer|mainframe]] computers, such as the [[Digital Equipment Corporation|DEC]] [[VAX]] and [[Data General Eclipse]]; however some computer families were based on proprietary components (e.g. Fairchild CTL) while supercomputers and high-end mainframes used [[emitter-coupled logic]]. They were also used for equipment such as machine tool numerical controls, printers and video display terminals, and as [[microprocessor]]s became more functional for "glue logic" applications, such as address decoders and bus drivers, which tie together the function blocks realized in VLSI elements. The [[Gigatron TTL]] is a more recent (2018) example of a processor built entirely with TTL integrated circuits.

=== Analog applications ===
While originally designed to handle logic-level digital signals, a TTL inverter can be biased as an analog amplifier. Connecting a resistor between the output and the input biases the TTL element as a [[negative feedback amplifier]]. Such amplifiers may be useful to convert analog signals to the digital domain but would not ordinarily be used where analog amplification is the primary purpose.<ref>{{citation |last=Wobschall |first=D. |title=Circuit Design for Electronic Instrumentation: Analog and Digital Devices from Sensor to Display |edition=2d |location=New York |publisher=McGraw Hill |year=1987 |isbn=0-07-071232-8 |pages=209–211}}</ref> TTL inverters can also be used in [[crystal oscillator]]s where their analog amplification ability is significant.

A TTL gate may operate inadvertently as an analog amplifier if the input is connected to a slowly changing input signal that traverses the unspecified region from 0.8&nbsp;V to 2&nbsp;V. The output can be erratic when the input is in this range. A slowly changing input like this can also cause excess power dissipation in the output circuit. If such an analog input must be used, there are specialized TTL parts with [[Schmitt trigger]] inputs available that will reliably convert the analog input to a digital value, effectively operating as a one bit A to D converter.

=== Serial signaling ===
'''TTL serial''' refers to [[single-ended signaling|single-ended]] [[serial communication]] using raw transistor voltage levels: "low" for 0 and "high" for 1.<ref>{{cite book|title=Signal and Power Integrity in Digital Systems: TTL, CMOS, and BiCMOS|year=1996|isbn=0070087342|url=https://books.google.com/books?id=6yRTAAAAMAAJ&q=single-ended+TTL-+or+CMOS-level+communication|page=200|last1=Buchanan|first1=James Edgar|publisher=McGraw-Hill }}</ref> [[Universal asynchronous receiver-transmitter|UART]] over TTL serial is a common debug interface for embedded devices. Handheld devices such as graphing calculators and {{nowrap|[[NMEA 0183]]-compliant}} [[Global Positioning System|GPS]] receivers and [[fishfinder]]s also commonly use UART with TTL. TTL serial is only a ''de facto'' standard: there are no strict electrical guidelines. Driver&ndash;receiver modules interface between TTL and longer-range serial standards: one example is the [[MAX232]], which converts from and to [[RS-232]].<ref>{{cite web |title=RS-232 vs. TTL Serial Communication - SparkFun Electronics |url=https://www.sparkfun.com/tutorials/215 |website=www.sparkfun.com}}</ref>

[[Differential TTL]] is TTL serial carried over a [[Differential signalling|differential pair]] with complement levels, providing much enhanced noise tolerance. Both [[RS-422]] and [[RS-485]] signals can be produced using TTL levels.<ref>{{cite web |title=B&B Electronics - Polarities for Differential Pair Signals (RS-422 and RS-485) |url=https://www.bb-elec.com/Learning-Center/All-White-Papers/Serial/%E2%80%A2-Polarities-for-Differential-Pair-Signals-%28RS-422.aspx |website=www.bb-elec.com}}</ref>

[[ccTalk]] is based on TTL voltage levels.