The LT terminal drives all display outputs on when the terminal is driven to logic 0 with the RBO terminal open or at logic 1. Note from Figure 1 that each of these ICs has three input ‘control’ terminals, these being designated LT (Lamp Test), BI/RBO, and RBI. The 74LS48 can be used to drive a seven-segment LCD display by using the connections already shown in last month’s Figure 11. The Rx resistors must limit the segment currents to less than 24mA in the 74LS47, and less than 6mA in the 74LS48. The 74LS48 has active-high outputs designed for driving a common-cathode LED display in a manner similar to that of Figure 2, but with the display’s common terminal taken to ground. Basic way of using a 74LS47 IC to drive a common-anode LED display. The 74LS47 has active-low outputs designed for driving a common-anode LED display via external current-limiting resistors (Rx), as shown in Figure 2.įIGURE 2. Functional diagram of the (a) 74LS47 and (b) 74LS48 BCD-to-seven-segment decoder/driver ICs. Figure 1 shows the functional diagrams and pin designations of these devices, each of which is housed in a 16-pin DIL package.įIGURE 1. They have integral ripple-blanking facilities, but do not incorporate data latches. These seven-segment decoder/driver ICs are members of the LS TTL family. The rest of this article describes a few of the most popular of these devices. Some of these devices have integral ripple-blanking facilities, others have built-in data latches, and a few even have built-in decade counter stages, etc. PRACTICAL DECODER/DRIVER ICsĭecoder/driver ICs are available in both TTL and CMOS forms.
This concluding episode deals with practical seven-segment decoder/driver ICs. The opening episode of this special feature explained the basic operating and usage principles of seven-segment alphanumeric displays.
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