Registers, Assignment of registers, Classification...

Register Assignment

A register is a sequential device executed on triggers of one type or another. Its main function is to store data (information) as an N-bit binary code. The binary code is fixed to N triggers. Entering new data in the register is called a write operation (recording), data output from register - reading operation (reading). The exchange of information between the register and external devices can occur in serial and (or) parallel codes.

Classification of registers

The method of record/read data distinguishes: sequential, parallel and combined registers.

Regarding the functional characteristic , registers are divided into two large groups:

• Storage registers that perform only one - the main function;

• shift registers , , performing, in addition to storage, a shift of information along the register. Among the registers of the last group, there are reversible registers that allow you to move information in both directions.

Consider the features of the main types of registers, illustrating the principles of their construction and operation for N = 4.

Serial registers

In registers of this type, writing and reading are performed in sequential code. During the write process, the data is put into flip-flops sequentially in time bit by bit, and when read, also bit by bit are output from the register. Serial registers have one information input X and one output Y, the entry C of the record/reading, the input R of the initial setup triggers the register to zero state (reset). During recording and reading, information is shifted (shifted) along the register. Therefore, sequential registers are also called shifting.

The scheme of the 4-bit register, built on D-flip-flops with asynchronous R-inputs, is shown in Fig. 3.27, a.

In the above circuit, the RS inputs are used to reset the register by feeding to each trigger signal R = 0, 5 1. =

The rules of the JV-bit register are shown in Table. 3.10. It should be borne in mind that n = 1, ..., JV - 1, the output <2 "for n = N - 1 is the output of the register (Fig. 3.27). Features of the main modes of the register:

Reset of the register is produced by the signal R = 0, while the state of the clock C and the information X

Fig. 3.27. Serial register schema (a) and the state of the input data, register flip-flops and output data in the write/reading (b)

can be any (Φ = 0 or 1). At the outputs of all triggers, a zero signal is set (& frac34; = Q, = 0);

Table 3.10

 Inputs Trigger Outputs Mode R C X 0 F F 0 0 Reset 1 0 Storage 1 1 Write-shift - read

• for R = 1, C = 0 the register is in the storage mode where the signals Q ^ _1 received at the previous clock cycle are stored at the outputs of the triggers. The state of the information input X can be any. The input signal X k to be written must be set in this mode, since the state of the trigger inputs is T 0 - T N _ t does not affect their outputs;

• for R = 1, C to = 1, the previously set input signal .X * -1 will appear at the output (& frac34; flip T0. the signal Q kn ~ _ will appear from the output of the trigger T n_ , which was written on (k - 1) -th step .Thus, for C k = 1, you can simultaneously write, move and read information.

The operation of the serial register in the write/read mode is shown in Fig. 3.27, b. In the initial state, the code 1001 was stored in the register. For four cycles, the code 1010 was written to the register, and code 1001 was written out of the register.

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