A standard set of subcircuits is provided with the logic simulator for designing logic circuits using standard TTL chips. The TTL family of integrated circuits was introduced about 20 years ago by Texas Instruments. TTL stands for Transistor Transistor Logic, which signifies that two transistors are used to drive each output of each chip, one for pulling the output down to alow level, and one for pulling the output up to a high level. Chips made using TTL technology are faster than the older RTL (Resistor Transistor Logic) and DTL (Diode Transistor Logic) families of integrated circuits, and they consume more power than the MOS (Metal Oxide Semiconductor) technology used in most VLSI (Very Large Scale Integrated circuit) chips.
The TTL family has at least 6subfamilies which offer different speed/power tradeoffs. These are summarized in the following table, where they are listed in roughly the order in which they were introduced:
family | | delay (ns) | power (mW) |
basic | | 10 | 10 |
low-power | L | 35 | 1 |
Schottky | S | 3 | 18 |
low-power Schottky | LS | 9 | 2 |
advanced Schottky | AS | 1.5 | 10 |
advanced low-power Schottky | ALS |4 | 1 |
The term Schottky refers to a technology for making faster transistors. It is interesting to note that, in each generation of the TTL family, the low power representative of that generation is about 3 times slower than the other member, but consumes about 1/10 the power. Today, the low-power Schottky subfamily is the most widely used member of the TTL family; chips from this family areavailable from a wide variety of manufacturers
All manufacturers of TTL chips use a common naming system, as exemplified by the chip name ``SN74LS00''. The prefix SN indicates that the chip was made by Texas Instruments; other manufacturers have their own prefix codes, but if the remainder of the chip name matches, the chips should perform exactly the same function. Additional one letter codesmay be added as prefixes or suffixes to this code, for example, RSN indicates radiation hardened chips made by Texas Instruments, and SNM indicates the use of quality control procedures specified by the military specification MIL-STD-883. The numeric code 74 indicates that the chip conforms to the requirements of the civilian computer industry, being able to operate over a temperature range of to C,while the code 54 indicates the ability to operate over the more extreme temperature range of to C required by many military and industrial applications. The letters LS indicate which subfamily the chip belongs to. Finally, the last two digits indicate the logical function performed by the chip.
Each Iowa Logic Specification Language TTL subcircuit description corresponds to one standard chip,and these chips are packaged one per file, in a form appropriate for inclusion using the use statement. The actual file names of these circuits will depend on your installation, but in general, the prefix indicating the manufacturer and military rating will not be included in the name, since it conveys nothing about the logical function of the chip. The following circuit descriptions are currentlyavailable (listed in numeric order):
LS00 Quad 2-input nand gates.
LS02 Quad 2-input nor gates.
LS04 Hex inverters.
LS08 Quad 2-input and gates.
LS10 Triple 3-input nand gates.
LS11 Triple 3-input and gates.
LS20 Dual 4-input nand gates.
LS21 Dual 4-input and gates.
LS27 Triple 3-input nor gates.
LS30 8-input nand gate.
LS32 Quad 2-input or gates.
LS42 BCD-to-decimaldecoder (or 3-line to 8-line decoder with enable).
LS74A Dual positive-edge-triggered D flipflop.
LS85 4-bit binary magnitude comparator.
LS86 Quad 2-input exclusive-or gates.
LS109A Dual positive-edge-triggered J- flipflop.
LS125A Quad bus-buffer gates with three-state outputs.
S133 13-input nand gate.
LS139 Dual 2-line to 4-line decoders/demultiplexers.
LS153 Dual 4-line to 1-line...