Engineering Dictionary of Terms
"A"
"B"
"C",
"D",
"E",
"F",
"G",
"H",
"I",
"J",
"K",
"L",
"M",
"N",
"O",
"P",
"Q",
"R",
"S",
"T",
"U",
"V",
"W",
"X",
"Y",
"Z"
IC Identity Comparator Chips
8-input Magnitude Comparator Circuit
Identity Comparator. This Identity Comparator can be used to perform comparisons of two 8-bit binary or BCD words. The output provides a P equals Q function. However unlike a Magnitude Comparator it does not provide a P greater than Q function. Note that most Magnitude Comparators supply the Identity Comparator function.
An Identity Comparator would be considered standard logic or glue logic when a discrete IC is used. However, because of the internal complexity, an Identity Comparator would also be considered an MSI Function [Medium Scale Integration].
Magnitude Comparator by Function:
Note in most cases when a 74xx device is listed, a 54xx device is also available.
74xx represents the commercial temperature range and 54xx represents the industrial temperature range [IC Part Number Prefix].
54LS85 4-Bit Magnitude Comparators
74ALS518 8-Bit Identity Comparators (P=Q) w/ Enable, Open Collector Outputs, 20K Ohm Q-Input Pullup Resistor
54ALS520 8-Bit Identity/Magnitude Comparators (P=Q) with Enable and 20K Ohm Q-Input Pullup Resistors
74F521 8-Bit Identity/Magnitude Comparators (P=Q) with Enable
54LS682 8-Bit Identity/Magnitude Comparators
54LS684 8-Bit Identity/Magnitude Comparators
54ALS688 8-Bit Identity/Magnitude Comparators (P=Q) with Enable
54AS885 8-Bit Magnitude Comparators
There is one military specification that references Identity Comparators; MIL-M-38510/347: Advanced Schottky TTL, 8-Bit Identity Comparator.
An Identity Comparator or Magnitude Comparator is used to compare to binary numbers, 8 bits in this example. A common application could be to receive a 8 bit address via a board-to-board connection and compare that address to an on-board setting to determine if the card was being addressed. Two comparators could be used to check a 16 bit address and four comparators could be used to check a 32 bit address. When the data [an address in this case] is valid and clocked into the flip flop is determined by another function which would clock in the data when required. However the determination of when data is valid would change depending on the board interface and protocol.
For reference you can also check out the transistor schematic of a 2-Input XOR Gate and includes a list of TTL ICs still in production.
