What Is Strobe Control Shift Register

Zoran Mijanovic & Nedjeljko Lekic

EDN

This Blueprint Idea shows how a single microcontroller port can bulldoze a lot of output lines through shift annals. In this instance we use the shift register with strobe control to achieve perfect output line control.

Shift register outputs can bulldoze LEDs, relays, etc. In other words, they can exist used equally (boosted) general purpose outputs.

Today there are shift registers that have Information and CLOCK inputs only, similar 74HC164, and shift registers with same inputs plus STROBE command input, like 74HC4094 or 74HC595. The shift registers without STROBE control have brusk-term transient states at outputs during shifting. Transients occur because shift register is directly continued to output lines. This kind of shift register can be used for driving LEDs and similar devices where curt-term transient is irrelevant. For example, the human eye can't notice LED flickers shorter than 10 msec. The shift registers with STROBE command have 2 registers.


Figure i.	*This is a logic diagram of the shift register with strobe input (74HC4094).*

The first one is shift register and the second one is storage register. The storage register keeps its data frozen while the new data are being loaded in shift register. After the new data is shifted in, STROBE pulse is used to transfer all data bits to storage register at in one case. In this way outputs are ready without transients. This is a new quality which makes this shift register applicable for driving transient sensitive devices similar TRIACs, super bright LEDs, etc.

In that location are several different solutions for driving shift register with few I/O lines. Some of the Design Ideas referenced below draw driving shift register without strobe control.

In lodge to explain how to drive shift register with STROBE control over only 1 I/O line we testify circuits from figures 2 to iv. Figure 2 shows shift annals controlled with three lines: Data, CLOCK, and STROBE.


Figure ii.	*The shift registers shown are controlled with three lines: Information, CLOCK, and STROBE.*

If STROBE control input is connected to 5V, logical ane, we practically get shift register without STROBE control. For such a example we can apply the solution from Article "Bulldoze sixteen LEDs with one I/O line", where one I/O line drives DATA and CLOCK input (Figure 3).


Figure iii.	*One microcontroller port controls DATA and CLOCK inputs of shift registers. The STROBE input is inactive, connected to 5V (logical one).*

But when we want to apply STROBE signal to get transient free output signals, information technology seems that we need 2 ports, CLOCK and STROBE. Farther comeback is possible by adding a monostable multivibrator circuit.

Finally, we propose the simplest solution. In this solution STROBE input is controlled over RCD network (Figure 4).


Figure four.	*The shift register (with STROBE input) is controlled over one I/O line, using RCD network.*

The RCD network is formed from discrete resistor Rn=220KΩ, capacitor Cn=47p, and diode Dn. The RCD network enables that STROBE signal rapidly drops to zero, but slowly ascent to ane with fourth dimension constant Rn×Cn=10.34 µsec.

Part 2 - How it Works