JPS63121922A - Barrel shift circuit - Google Patents

Abstract

PURPOSE:To shift continuous words by extracting data equivalent to one-word which should be actually written in a memory after data of two words adjacent to each other is given as the input and is shifted by data equivalent to two words. CONSTITUTION:A second barrel shift circuit 2 is provided to take out the input, which should be allowed to correspond to idle bits, from a second word, and bits overflowed from the second input word by the shift processing of the second barrel shift circuit 2 are allowed to correspond to idle bits due to the shift processing of a first barrel shift circuit 1. As the result optical continuous bits equivalent to one-word are selected from first and second input words by the shift processing to obtain one output word.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bitmap display device, and particularly to a barrel shift circuit suitable for display memory control when copying or moving a figure on a display screen to another position.

[Conventional technology]

In conventional bitmap display devices, the NECrPC-
100? It is equipped with a barrel shift circuit as shown in "Nical Manual", page 5-5. This is used to shift one word of data read from the bitmap memory by a specified number of bits, write the shift result back into the bitmap memory, and move graphic data bit by bit. When the barrel shift circuit receives 17-word data, it outputs the data that has been shifted by a preset number of bits, so by writing the output of the barrel shift circuit to the bitmap memory, the data in one word can be changed. The position of each bit can be shifted. However, no consideration has been given to the case where graphic data having an area exceeding one word is moved.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into account the shift processing of data spanning multiple words, and there is a problem in that valid data is not reflected in empty bits generated by the shift.

An object of the present invention is to solve this problem, and when shifting data spanning multiple words, a barrel shift circuit enables shifting of consecutive words by reflecting the bits of adjacent words in the empty bits generated by the shift. Our goal is to provide the following.

[Means for solving problems]

The above purpose is to input two adjacent words of data as input to the barrel shift circuit, perform shift processing for two words, and then data for one word that needs to be actually written into memory. This is achieved by extracting the .

[Effect]

The barrel shift circuit of the present invention includes a first barrel shift circuit that shifts the first word and a second barrel shift circuit that shifts the @2 word.

The first barrel shift circuit selects bits corresponding to each bit of the output word from the first input word according to the given number of shift bits, and outputs the selected bits.

In this case, if the shift direction is left, the right side of the output word,
When the shift direction is right, empty bits that do not correspond to input bits are generated on the left side of the output word. In conventional barrel shift circuits, the bits that overflow from the input word are made to correspond to these empty bits through shift processing, and
A process called bit rotation, or rotation, was realized. In contrast, in the present invention, the 20th barrel shift circuit provided for extracting the input corresponding to the empty bit from the second word is biased, and the second input word is shifted by the shift processing of the 20th barrel shift circuit. The bits overflowing from the 10th barrel shift circuit are made to correspond to empty bits generated by the shift process of the 10th barrel shift circuit. As a result, 1.
From the second input word, bits for one arbitrary continuous word can be selected by shift processing and can be made into one output word.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, 1 is the first
0 barrel shift circuit; 2 is a second barrel shift circuit that shifts the second input word; 3 is a decoder that provides the amount of bits to be shifted as a binary value to the barrel shift circuit; 1
0 to 17 are selectors configuring the barrel shift circuit 1, and 2
0 is a selector configuring the barrel shift circuit 2.

In the following, for the sake of simplicity, one word will be explained as having four bits, and the barrel shift circuit will be explained as being in the left direction in the figure, but it is clear that the same argument can be made in the case of other word configurations or right shift.

In FIG. 1, selectors 10 to 17 and 20 connect the signal to the input terminal to the output terminal Y when the input value of the switching terminal S is a logical value "0", and the input value of the switching terminal S is a logical value. When "1", the signal at input terminal B is connected to output terminal Y. In addition, the TTL 2 child Toshite, Hitachi Ribyo mTTL, 74LS157 or 7 with such functions
4L8257 and equivalent products can be used.

In FIG. 1, decoder 3 provides barrel shift circuits 1 and 2 with the number of bits to be shifted. Assuming 1 word is 4 bits, the number of bits to shift is Q, 1.2
．． Three bits are valid, and the decoder 3 supplies them as a two-bit binary signal to the barrel shift circuit t2. That is, when the number of pits to shift is 00, bl=
0. When bO=0.1, bj=Q; when bQ=1.2, b1=1. When bO=0.5, b1=1. bO=1
becomes. Since the selectors 14 to 17 and 20 input the signal b1 given from the decoder 5 to the switching terminal S, b
When 1=0, input terminal A, when b1=1, input terminal B
Connect to output terminal Y. The first and second input words are shifted to the left by selectors 14-17 and 20 by 0 bits when b1=o and by 2 bits when bl-J. Similarly, the output signals of selectors 14 to 17 and 20 are
Selectors 10 to LIC shift left by 0 bit when bO=0 and by 1 bit when b1=1, and as a result, selectors 14 to 17 and 20 and selectors 10 to 13
By integrating the shift amounts, it is possible to shift o,t2.3 bits. Due to the left shift operation of the barrel shift circuit 1, empty bits are normally generated in the right side of the first input word, but in this embodiment, the second input word and the barrel are placed in the portion where the empty bits occur. Since the output of shift circuit 2 is connected, the first. A shift operation can be performed across the second input word K. Further, the barrel shift circuit 1 and the decoder 5 have the same configuration as a conventional barrel shift circuit, and the barrel shift circuit 2 is the only additional circuit required to implement the present invention.

In the embodiment shown in FIG. 1, only the selector 20 constitutes the barrel shift circuit 2, and the present invention can be implemented at low cost.

Generally, if one word is 2n bits, n x 2" selectors are required to configure the barrel shift circuit 1. On the other hand, to configure the barrel shift circuit 2, (2" - n-1) selectors are required. Comparing the ratio between the two, for example, when n=5, it is 24:
4. When n=4, 64:11. When n=5, 1(5
0:26, so there is little increase in the number of parts due to the addition of the barrel shift circuit 2.

FIG. 2 is a block diagram showing another embodiment of the invention.

In FIG. 2, the same circuit parts as in FIG. 1 are given the same numbers. In FIG. 2, reference numeral 4 denotes an input switching circuit 40 to 42 for switching the input word to be applied to the barrel shift circuit 12.
is a selector forming the input switching circuit 4. In FIG. 2, the circuit operations of barrel shift circuit 12 and decoder 30 are exactly the same as in the embodiment of FIG. The input switching circuit 4 switches and supplies the first or second input word to one of the two input words applied to the barrel shift circuit 1.2. When the input switching circuit 4 selects the second input word and connects it to the output terminal Y, the circuit operation of the embodiment of FIG. 2 is completely the same as the embodiment of FIG. 1 as a whole. When the input switching circuit 4 selects the first input word, 27- input to the barrel shift circuit t2
The data of both words become the first input word. As a result, the barrel shift circuit 2 fills in the empty bits generated by the shift operation of the barrel shift circuit 1 with the bits overflowing from the first input word, and the output word becomes the rotated first input word. Become. As described above, in the embodiment of FIG. In addition to shifting across the second input word, rotation within the first input word can be performed.

In the embodiment shown in FIG. 2, the input switching circuit 4 is connected to the selectors 14 to 17 and the 200 Å power terminal B (II), but the same effect can be obtained by connecting the input switching circuit 4 to the input terminal A side. Furthermore, if an input switching circuit is provided for both input terminals A and B, the adjacency relationship between the first and second input words can be switched and used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to shift input data bit by bit across two words K and extract a bit string for one word starting from an arbitrary bit position. The effect is that graphic data on the map memory can be copied and moved quickly and efficiently. In addition, the increase in circuit scale required to implement the present invention is small (and can be implemented at low cost. In particular, the present invention can be realized by integrating a single element, so it is suitable for LSI implementation. , - layer circuit scale and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a simple example of the present invention, and FIG. 2 is a block diagram showing another embodiment of the present invention. 1... Barrel shift circuit, 2... Barrel shift draw path, 3... Decoder, 4... Input switching circuit. Akira Kuni/A input hood name 2 (71 pieces Coward Akira 20

Claims (1)

[Claims] 1. A barrel shift circuit that receives a binary logic signal with predetermined weighting, shifts it left or right by a specified number of bits according to the weighting of each signal, and outputs the shifted signal,
Empty bits that occur when inputting the first and second word logic signals simultaneously and shifting the first word logic signal to the left or right, relative to the number of bits of the logic signal for one word to be output In contrast, the barrel shift circuit is characterized in that the bit signal that overflows when the logic signal of the second word is shifted in the same direction as the shift of the first word is compensated for to provide a shift output for one word. 2. A selection circuit is provided in at least one of the terminals for inputting the logic signals of the first word and the second word, and the selection circuit inputs the logic signals of the first word and the second word, and the selection circuit inputs the logic signals of the first word and the second word. 2. The barrel shift circuit according to claim 1, wherein the logic signal of the second word is switched and used as an input signal of the barrel shift circuit.