54/74 series logical chips

1 54/74 series circuits are commonly used logic circuits in digital circuits. 54 are military standards, 74 are commercially available for civil use, but their circuit functions are the same.

2 ls the open circuit input is a high level, HC input does not allow open circuit, HC generally requires the upper drop-down resistance to determine the input is invalid level, but ls does not have this requirement.

3 ls pull-down is strongly pulled up, while HC pull-up and pull-down are the same (understanding is the strength of the drive current)

4. The operating voltage is different. The ls can only use 5 V, while the HC generally uses 2 V to 6 v;

5. Different logic levels. Ls is a TTL level, and its low-level high-level demarcation value is 0.8 V, 2, 4 V, respectively. When the HC operating voltage is 5 V, the low-level high-level demarcation value is 3.6 V and V. The CMOS logic gate circuit can drive the TTL logic gate circuit.

6. Different driver capabilities. Generally, the LS high-level drive capability is 5mA, while the low-level drive capability is 20mA at a low-level, and the CMOS High-Level drive capability is 5mA.

7. The circuit with CMOS structure has poor antistatic capability and is prone to plug-in locks. Therefore, the input foot of CMOS cannot be connected to the power supply;

The 8-74 series are classified into TTL and CMOS.

9 74 TTL type: 74xx (standard type); 74 lsxx (low-power type); 74sxx (low-power type); 74 alsxx (Advanced Low-power type ); 74 asxx (advanced type); 74fxx (high-speed type );

10 74 series high-speed CMOS is divided into three categories: 74 hcxx (CMOs operating level); 74hct (CMOs TTL level); 74 hcuxx (no buffer );

11. For 74 series products, if the number of logical functions is the same, the functions are the same.

12 if the power supply voltage is 3 V, select 74hcxx type; when the power supply voltage is 5 V, select 74lsxx type.

13 typical electrical parameter values of common types