Latching circuit

A latching circuit waits for an event to occur. Once that event occurs, the latch output changes state and will ignore any further events until reset. This can be described as a memory element. The latch has many applications in the system. For example, if a failure mode occurs in the system, a shutdown signal may be sent to the latch circuit, which will shut down the system and prevent any further possible damage. The system will remain shut down until the power to the system is recycled. 

One functional gate dielectric of interest to a number of groups is using a ferroelectric material to retain state in transistor devices. This has a range of applications including latching circuits [97] and memory storage elements... 

Sheet 1 shows the summation of the sub-safety circuit relaying on the VSR power supply battery and the latching circuit Also shown is the... 

The latch circuit shown in Fig. 1.56(c) is redrawn in Fig. 1.58 with the outputs represented in terms of the inputs, with the gate delay explicitly shown, and with the outputs expressed as first-order difference equations in terms of the inputs. The case for general inputs is shown in Fig. 1.58(a) and the special case for low inputs in Fig. 1.58(b). With low inputs the equations in Fig. 1.57(b) show that if the two outputs are complements, O2 = 0[, that the system is stable, that is, 0 = 0[ and = O - It also shows that if the two outputs are equal O2 = 0[ the system is unstable, that is, = 0 and = O. Table 1.22 illustrates the development for the low input cases. 

FIGURE 1.63 The JK latch (a) JK latch circuit, (b) JK latch SBS representation, (c) JK latch truth table. 

Now let s look at the coils inside the relay. The coils in the relay are normally DC activated only through a bridge rectifier, (see circuit drawings of AC relays and note the diamond shaped symbol for a bridge rectifier). They function as a switch to open the circuit, which stays open as long as the inverter is turned on. (one Click). If the relay is working on AC current it will buzz as the latching is switched back and forth. 

Based on this design a memory/adder model (Fig. 6(c)) using 464 transistors could be constructed and evaluated on grounds of SPICE circuit simulations. Four bits of information were read from four different memory cells, added as two 2-bit words, and the resulting 2-bit was moved through registers (clocked D-latches) to a subsequent computation. It must be noted... 

The variable Fox is not assigned in the else-branch of the conditional statement. Consequently, a latch is inferred for Fox since it needs to retain its value when Sat is true. The circuit synthesized in shown in Figure 1-10. 

When a disconnect switch, circuit breaker, or set of fuses is included in the same enclosure as the contactor, the starter is then called a combination starter. In addition to the fault-current-interrupting function, the breaker or fuses serve as the disconnecting device. Figure 29-5 illustrates schematically combination starters of various types. The latch is arranged to open the disconnect before the door can be swung open. There are also provisions for padlocking the disconnect open with the door closed so that maintenance wonc on the motor may proceed in safety. 

The construction of such circuits is also quite easy. The knobs operate variable resistors which feed variable voltages into a multiplexed ADC. The latter should have a latched output, i.e., it should put out the last value converted until the new conversion. The speed of the ADC is not critical and you can use an inexpensive one. 

Fig. 7.1. Two architectures for display driving, (a) shows a single transistor architecture appropriate for latching and holding charge on the pixel for field driven display elements such as liquid crystal displays or e-Ink. (b) schematically shows the matrixed version of this element, (c) shows a two transistor voltage-programmed current driver appropriate for OLEDs. More advanced voltage and current programmed circuits are also possible, but require more transistors.

In a voltage programmed drive circuit, the voltage on the gate of the drive transistor is driven directly and latched through switches on the backplane. While relatively simple to implement, this has several disadvantages ... 

An alternative approach is the use of a current drive, in which a programming current is latched in the cell. One approach is to build a current mirror in which one arm is driven through a dummy load and then latched to the other arm (containing the OLED) each cycle. This linearizes the drive in current and also compensates for some spatial variation across the panel. Yet another approach is to drive the latching element itself and sustain the driven current. While complicated from a circuit perspective, this approach has the greatest potential for degradation compensation. Several architectures and their modeling are explored in [135]. 

Latches can, of course, be constructed for any number of data bits. Integrated-circuit data latches are commonly available in 4-bit, 8-bit, and larger configurations. 

At all reactors but C, there are two complete systems in the 3XX circuit. TWO batteries, two sets of pressure switches, and two latching solenoid mschanisms will allow failure of a single system without the consequence of a "ball drop" A manual pushbutton is located centrally in each control room to trip both systems, thus dropping the balls. Modifications are presently underway at C Reactor to Install a dual system similar to the other reactors. 

The nuclear fission chain reaction within the tank 80 is controlled by a neutron absorbent control rod 98 re- 30 ciprocable within a permeable tube 100 formed of a material such as beryllium having a small neutron capture cross section, and the rod 98 is actuated by a rack and pinion mechanism 102. Emergency control of the reaction is provided by a neutron absorbent control rod 104 35 disposed within a neutron permeable tube 106 and held in the retracted position shown in FIG. 3 by an electrically operated latch 1C8. Under emergency conditions, the latch is released and the rod 104 is drawn into the central portion of the system by means of a weight 110 con- 40 nected to the rod 104 by a line 112 supported by a pulley 114. The neutron density within the system is monitored by a conventional ionization chamber 116 connected in a conventional manner to an electrical circuit (not shown) for measuring the neutron density. 45... 

When propagated, the pulse hits the sequential latch window on the sequential logic to the right, which registers the incorrect value 0 , instead of a 1 . Such effects may be masked by the circuit, as discussed in the following subsections. 

Faults can also be masked by three different ways in the circuit logical masking, electrical masking and latch window masking. Figures 2.3, 2.4 and 2.5 show each of them, respectively. 

The memory elements of the circuit (flip-flops and latches), called registers, are all loaded synchronously with a clock edge at the clock edge, a register loads its next value, which then becomes its current value until the next clock edge registers hold the state of the machine. 

Blif-mv consists of symbolic hardware, where high level objects are modeled either by wires, if they are non-memorising, or latches, if they are memorising. These objects are very close to those found in Verilog. Blif-mv also contains so called multi-variables, which is a representation of enumerated variables. The next value of latches is the output wire of a circuit representation of the transition function. In Blif-mv, all objects are scalar, and all functions are either a subcircuit (a network of more elementary functions) or a function given in tabular form. No predefined function exists. 

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