TTL
"Transistor Transistor Logic"
Basic voltage levels
VOHmin (minimum HIGH output voltage) 2.4V
VOLmax (maximum LOW output voltage) 0.4V
VIHmin (minimum HIGH input voltage guaranteed to be recognised as logic 1) 2V
VILmax (maximum LOW input voltage guaranteed to be recognised as logic 0) 0.8V
Power
Draw a lot of power (individual gates may draw 3 to 4 mA).
Low power Schottky versions of TTL chips (LS) draw only 20% of the power, but are more expensive.
Inputs
TTL low input sources current into whatever drives it (0.25mA for LS), so whatever is pulling it low must be able to sink current <<<THIS IS A CLASSIC ISSUE TO OVERLOOK!
Outputs
Outputs are saturated transistor to ground in LOW and a darlington follower in HIGH (2 diode drops below V+).
For any TTL or CMOS family, any output should drive at least 10 inputs.
CMOS
"Complementary Metal Oxide Semiconductor Logic"
There are equivalents to most of the TTL chips, with CMOS devices having a 'C' in the middle of the part number: e.g. the 74C04 is the CMOS equivalent to the TTL 7404.
Basic voltage levels
VOHmin (minimum HIGH output voltage) 4.9V
VOLmax (maximum LOW output voltage) 0.1V
VIHmin (minimum HIGH input voltage guaranteed to be recognised as logic 1) 3.5V
VILmax (maximum LOW input voltage guaranteed to be recognised as logic 0) 1.5V
Power
Much lower in power requirements (drawing about 1 mA).
Operate with a wide range of supply voltages (3 to 18 volts).
Inputs
CMOS draws no input current.
CMOS input threshold usually 1/3 to 2/3 the supply voltage.
Outputs
Outputs are MOSFET and therefore rail to rail.
For any TTL or CMOS family, any output should drive at least 10 inputs.
Family Part Numbers
TTL
74 (no letters, e.g. 7400)
TTL
74LS
Early TTL low power Schottky. Improved 7400
74ALS
Higher speed, lower power TTL than LS
74AS
74F00
High speed Fast TTL improvement on LS
CMOS
4000B
Classic CMOS family. Static sensitive 3v to 15v supplies. 0.4mA source sink drive current.
74C
3 to 15 VCC
74HC
2.0 to 6.0 VCC
4mA/6mA Sink/Source
Basic high speed CMOS similar to TTL.
THE HC IS THE BASIC SIMPLE LOGIC GATE CHOICE FOR MANY APPLICATIONS
74HCT
4.5 to 5.5 VCC
4mA/6mA Sink/Source
The HCT and ACT CMOS families are designed with a low threshold similar to TTL for compatability (since bipolar TTL outputs do not swing all the way to +V).
74AC
2.0 to 6.0 VCC
24mA Sink/Source drive current.
74ACT
4.5 to 5.5 VCC
ACT has TTL compatible inputs.
Min high level voltage = 2V so these can be used to interface 3V3 IC’s to 5V IC’s.
The HCT and ACT CMOS families are designed with a low threshold similar to TTL for compatability (since bipolar TTL outputs do not swing all the way to +V).
74ABT
64mA per output, low noise
74FCT
CMOS. Bus interface devices. Lower power than 74F due to CMOS technology.
64mA, 48mA Sink Current Capability
74LV
CMOS 3.3v supply
74LVC
CMOS 3.3v supply, faster improved output over LV
74VHC