The designation TTL is sometimes used to mean TTL-compatible logic levels, even when not associated directly with TTL integrated circuits, for example as a label on the inputs and outputs of electronic instruments.

The design of the input and outputs of TTL gates allowed many elements to be interconnected.

Push – pull outputs are present in TTL and CMOS digital logic circuits and in some types of amplifiers, and are usually realized as a complementary pair of transistors, one dissipating or sinking current from the load to ground or a negative power supply, and the other supplying or sourcing current to the load from a positive power supply.

Pull-up resistors may be used at logic outputs where the logic device cannot source current, such as open-collector TTL logic devices.

The 7407 TTL device, an open collector buffer, simply outputs whatever it receives as input, but as an open collector device, the output is left effectively unconnected when outputting a " 1 ".

The tracert ( traceroute ), Pathping commands are implemented by transmitting UDP datagrams with specially set IP TTL header fields, and looking for ICMP Time to live exceeded in transit ( above ) and " Destination unreachable " messages generated in response.

* The TTL field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue.

They are activated by AC control signals or DC control signals from Programmable logic controller ( PLCs ), PCs, Transistor-transistor logic ( TTL ) sources, or other microprocessor and microcontroller controls.

Nameservers may also have a TTL set for NXDOMAIN ( acknowledgment that a domain does not exist ); but they are generally short in duration ( three hours at most ).

Newer DNS methods that are part of a DR ( Disaster Recovery ) system may have some records deliberately set extremely low on TTL.

For example a 300 second TTL would help key records expire in 5 minutes to help ensure these records are flushed world wide quickly.

TTL values are " per record " and setting this value on specific records is normally honored automatically by all standard DNS systems world-wide.

Mutable ( and therefore unauthenticated ) IPv4 header fields are DSCP / TOS, ECN, Flags, Fragment Offset, TTL and Header Checksum.

TTL chips are now are also made in surface-mount packages.

Successors to the original bipolar TTL logic often are interchangeable in function with the original circuits, but with improved speed or lower power dissipation.

TTL inputs are the emitters of a multiple-emitter transistor.

TTL inputs are sometimes simply left floating to provide a logical " 1 ", though this usage is not recommended.

Designers can combine ECL and TTL devices in the same system to achieve best overall performance and economy, but level-shifting devices are required between the two logic families.

The TTL " totem-pole " output structure often has a momentary overlap when both the upper and lower transistors are conducting, resulting in a substantial pulse of current drawn from the power supply.

V < sub > CC </ sub > and Ground are carryovers from TTL logic and that nomenclature has been retained with the introduction of the 54C / 74C line of CMOS.

The increased low output level can cause troubles when TTL logic circuits are driven.

Schottky metal – semiconductor junctions are featured in the successors to the 7400 TTL family of logic devices, the 74S, 74LS and 74ALS series, where they are employed as clamps in parallel with the collector-base junctions of the bipolar transistors to prevent their saturation, thereby greatly reducing their turn-off delays.

Going on these figures alone TTL logic gates are limited to perhaps 2 to 10, depending on the type of gate, while CMOS gates have DC fan-outs that are generally far higher than is likely to occur in practical circuits ( e. g. using NXP Semiconductor specifications for their HEF4000 series CMOS chips at 25 ° C and 15 V gives a fan-out of 34 thousand ).

The 7400 series of transistor-transistor logic ( TTL ) integrated circuits are historically important as the first widespread family of TTL integrated circuit logic.

An integrated circuit made in CMOS is not a TTL chip since it uses field-effect transistors ( FETs ) and not bipolar junction transistors, but similar part numbers are retained to identify similar logic functions and electrical ( power and I / O voltage ) compatibility in the different subfamilies.

Power supplies on the bus were unregulated + 8 V and ± 18 V, designed to be regulated on the cards to + 5 V ( used by TTL ) and ± 12 V ( typically used on RS-232 lines or disk drive motors ).

To limit the impact of DNS poisoning typically a TTL of 0 is used.

Older systems such as TTL used 5 volts, newer computers typically use 3. 3 volts ( LV-TTL ) or even 1. 8 volts.

These services can include voice ( plain old telephone service ( POTS ) or voice over IP ( VoIP )), data ( typically Ethernet or V. 35 ), video, and / or telemetry ( TTL, ECL, RS530, etc.

TTL became popular with electronic systems designers after Texas Instruments introduced the 5400 series of ICs, with military temperature range, in 1964 and the later 7400 series, specified over a narrower range, and with inexpensive plastic packages in 1966.

Time to live ( TTL ) is a mechanism that limits the lifespan or lifetime of data in a computer or network.

All modes use TTL voltage logic levels, which limits the possible cable length to a few meters unless expensive special cables are used.

Since the transistors of a standard TTL gate are saturated switches, minority carrier storage time in each junction limits the switching speed of the device.

A TTL input signal is defined as " low " when between 0 V and 0. 8 V with respect to the ground terminal, and " high " when between 2. 2 V and 5 V ( precise logic levels vary slightly between sub-types and by temperature ).

In some cases ( e. g., when the output of a TTL logic gate needs to be used for driving the input of a CMOS gate ), the voltage level of the " totem-pole " output stage at output logical " 1 " can be increased up to V < sub > CC </ sub > by connecting an external resistor between the V < sub > 3 </ sub > collector and the positive rail.

Like most integrated circuits of the period 1965 – 1990, TTL devices were usually packaged in through-hole, dual in-line packages with between 14 and 24 lead wires, usually made of epoxy plastic ( PDIP ) or sometimes of ceramic ( CDIP ).

Due to the output structure of TTL devices, the output impedance is asymmetrical between the high and low state, making them unsuitable for driving transmission lines.

Connecting a resistor between the output and the input biases the TTL element as a negative feedback amplifier.

The original Apple IIc motherboard ( manufactured between April and November 1984 ) derived the timing for its two serial ports through a 74LS161 TTL logic chip.

** 74-the " standard TTL " logic family had no letters between the " 74 " and the specific part number.

In the DUNDi configuration one can limit the number of consecutive lookups between peers by setting the TTL.

Wireless World magazine ran a series of articles between November 1975 and June 1976 describing the design and construction of a teletext decoder using mainly TTL devices ; however, development was limited until the first TV sets with built-in decoders started appearing in 1977.

It has a voltage swing between 0. 4 volts and 1. 2 volts — much lower than that used in TTL and CMOS logic — and symmetrical parallel resistive termination.