DISPLAY APPARATUS

Abstract: Display data is read out from a display memory (2) and is written into a buffer memory (8). In a time-division relation­ ship with this writing operation, display data is read out from the buffer memory (8). Smoothing is provided by the use of both the display data read out from the buffer memory (8) and the display data read out from the display memory (2).

Description: This invention relates to display apparatus, for instance display apparatus which may be used to display teletext, videotex and like information. It is known, in television broadcasting, to employ a television character multiplexing broadcasting technique in which the vertical blanking periods or intervals of a main television programme are utilised to broadcast various kinds of information such as news, weather forecast, notices and so on. A receiver for receiving such a broadcast may include a display apparatus constructed as shown in Figure 1 of the accompanying drawings. As shown in Figure 1, when pattern data to be displayed is received, it is processed by a central processing unit (CPU) 1 and then written to a pattern or display memory 2. In Figure 1, addresses Axy of the pattern memory 2 are shown schematically in correspondence to a display picture screen. A horizontal address (address in the horizontal direction) Ax corresponds to the horizontal scanning position of the display picture screen, a line address (address in the vertical direction) Ay corresponds to the vertical scanning position or the horizontal line (scanning line), and the condition Axy = a . Ay + Ax is established, in which a corresponds to the lateral width of the display picture screen and, for example, a = 32. Each bit in the memory 2 corresponds to each dot of a displayed pattern, a bit having level "1" being displayed as a dot (bright point). A control circuit 6 generates an address signal which designates the horizontal address Ax, namely a horizontal address signal HAS which is incremented by one for every byte (8 bits) of the pattern data in synchronism with the horizontal scanning, and an address signal which designates the line address Ay, namely a line address signal LAS which is incremented by one at every horizontal scan. The memory 2 is addressed by the address signals HAS and LAS and pattern data is read out byte by byte with the address corresponding to the scanning position of the display picture screen. The pattern data thus read out is loaded in parallel, byte by byte, into a shift register 3 and then serially outputted bit by bit therefrom. The pattern data thus outputted is supplied to a cathode ray tube (CRT) display 5. Accordingly, a pattern which corresponds to the bit image of the memory 2 is displayed on the screen of the CAT display 5. When such display is carried out, in order to make the displayed pattern easy to see it has been proposed to carry out smoothing (rounding) as disclosed, for example, in Japanese Examined Patent Application Publication No. JP-B-53-41016 and in corresponding US Patent No. US-A-3 878 536. Figure 2 of the accompanying drawings schematically shows an example of pattern data representing the character "A" written in the pattern memory 2. In this pattern data, the hatched bits represent level "1", while the bits without hatching represent level "0". Figure 3 of the accompanying drawings shows the character "A" displayed on the screen of the CRT display 5 with no smoothing having been carried out. References L1 to L14 designate lines (scanning lines), the scanning lines represented by solid lines being formed during odd field periods and the scanning lines represented by broken lines being formed during even field periods. The character is made up from dots Du (hereinafter referred to as "unit dots") having a fundamental size. Since the pattern data (Figure 2) in the memory 2 is used during both the odd and even field periods, the display pattern becomes as shown in Figure 2. When, on the other hand, smoothing is carried out, the character "A" is displayed as shown in Figure 4 of the accompanying drawings, in which half dots Dh having a width one half that of the unit dots Du are added to the display pattern of Figure 3. Accordingly, as compared with the character "A" which is not subjected to the smoothing as shown in Figure 3, the character of Figure 4 becomes smoother and easier to view. When the above-described smoothing is carried out, the half dots Dh are combined with the unit dots Du fundamentally in two ways, as shown in Figure 5 of the accompanying drawings, and in all patterns the half dots Dh are added to the unit dots Bin in the combinations shown in Figure 5. That is, when two unit dots Du are adjacent one another in an oblique (diagonal) direction, two half dots Dh are added in a direction intersecting the above-mentioned oblique direction. Accordingly, when the smoothing processing is carried out, during an odd field period both the pattern data on the line (the line address Ay of the memory 2 for an address n) which is currently displayed and the pattern data on the preceding line (Ay = n - 1) are required, while during an even field period both the pattern data on the line (Ay = n) which is currently displayed and the pattern data on the succeeding line (Ay = n + 1) are required. For this reason, when the smoothing is carried out, access to the pattern data in the pattern memory 2 is generally carried out as shown in Figure 6 of the accompanying drawings. Figure 6 shows a certain horizontal period, in which Tb represents horizontal blanking periods, Th represents a horizontal display period (horizontal scanning period), and Tp represents a period which corresponds to the lateral width of one byte of pattern data (see Figure 1). The horizontal address Ax (the signal HAS) is incremented by one address at every period Tp in response to the horizontal scanning position, while the line address Ay (the signal LAS) is designated as an address n' in a first half period Tpf of the period Tp and an address n in the second half period Tpb thereof, where n represents the line address Ay (= n) corresponding to the line which is currently displayed and n' is given by n' = n - 1 for odd field periods and n' = n + 1 for even field periods. In consequence, the data read from the memory 2 during the second half period Tpb is the pattern data (hereinafter simply called "display data DD") for the line (Ay = n) which is currently displayed, and the data read from the memory 2 during the first half period Tpf is the pattern data (hereinafter called "comparing data DR") for the preceding or succeeding line (Ay = n - 1 or Ay = n + 1). These data DD and DR are loaded into shift registers 3D and 3R as shown in Figure 7, via a data bus connecting the memory 2 to the shift registers, and then made simultaneous with each other. Then, the data DD and DR thereby made simultaneous with each other are subjected to smoothing process in a processing circuit 4, which produces a luminance signal having the half dots Dh as shown in Figure 5, which signal is delivered to the CRT display 5. However, in effecting such smoothing processing, since the memory 2 is always addressed by the control circuit 6 for reading during the horizontal display periods Th, the CPU 1 can access the memory 2 only during the horizontal blanking periods Tb. Thus, the waiting or latency time of the CPU 1 (the time during which it must wait for access to the memory 2) is long and the apparent processing speed and processing ability of the CPU 1 are thus lowered, which is inconvenient. If the period (Tpf + Tpb) is made shorter than the horizontal blanking period Tp, the CPU 1 can access the memory 2 during the remaining period. Processing in this manner would require the memory 2 to be an extremely high speed memory, which is difficult to realise. Even if such a high speed memory can be realised, it is very expensive. In order to obtain the comparing data DR, the line address Ay indicated by the line address signal LAS must be an address n' which is displaced by one address from the address n and its value n' becomes different in the direction of displacement depending on whether the field period is odd or even, whereby it is necessary to provide a complex address converting circuit. It will be seen that the arrangement described above with reference to Figures 6 and 7 comprises a display apparatus comprising a display memory having a capacity of a plurality of lines corresponding to effective raster scanning lines of a display, control means for controlling storage of display data in the display memory, and a smoothing processing circuit arrangement operative to carry out a smoothing processing operation based upon data of two adjacent lines read from the display memory. According to the present invention there is provided a display apparatus comprising a display memory having a capacity of a plurality of lines corresponding to effective raster scanning lines of a display, control means for controlling storage of display data in the display memory, and a smoothing processing circuit arrangement operative to carry out a smoothing processing operation based upon data of two adjacent lines read from the display memory, the apparatus being characterised in that a buffer memory having a capacity of one said line is provided and in that the control means is so operative that, during a first period, the display data is read from the display memory and written to the buffer memory, while, during a second period which does not overlap with the first period, the display data is read from the buffer memory and the smoothing processing is carried out by the smoothing processing circuit arrangement on the basis of the display data read from the display memory and the display data read from the buffer memory. A display apparatus embodying the invention and described hereinbelow is capable of reducing the waiting or latency time of a CPU caused by the smoothing processing without needing to incur the increase in cost resulting from the use of a high speed pattern memory. The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which like references indicate like items through the various figures, and in which: Figure 1 is a block diagram of a previously proposed display apparatus; Figure 2 shows schematically an example of pattern data, representing the character "A", written in a pattern memory of the apparatus of Figure 1; Figure 3 shows the character "A" as displayed, without smoothing, on the screen of a CRT display of the apparatus of Figure 1; Figure 4 shows the character "A" as displayed on the screen with smoothing; Figure 5 shows two different ways in which half dots are added to unit dots to produce a smoothed display; Figure 6 represents a horizontal period, including a horizontal display period and horizontal blanking periods, and is used in explaining how the pattern memory is accessed to provide a smoothed display; Figure 7 is a block diagram of a display apparatus which corresponds to that of Figure 1, but which includes further components for achieving a smoothed display; Figure 8 is a block diagram of a display apparatus embodying the present invention; Figures 9A and 9B represent, for odd and even fields respectively, a horizontal period, including a horizontal display period and horizontal blanking periods, and is used in explaining the operation of the apparatus of Figure 8; and Figure 10 represents the contents of a pattern memory and a buffer memory of the apparatus of Figure 8 during operation. A display apparatus embodying the invention will now be described with reference to Figures 8 to 10. The apparatus will first be described in outline and then described in more detail. In outline, the display apparatus embodying the invention includes, as shown in Figure 8, a buffer memory 8 having a capacity of one line. During each period Tpb (forming part of a period Tp) pattern data is read from the pattern memory 2 and is written to the buffer memory 8, while during each period Tpf (also forming part of a period Tp) the pattern data is read from the buffer memory 8. Then, the smoothing processing is carried out on the basis of the pattern data read from the pattern memory 2 during the period Tpb and the pattern data read from the buffer memory 8 during the period Tpf. Consequently, since the CPU 1 can access the memory 2 during the period Tpf, it is possible considerably to reduce the waiting or latency time of the CPU 1. Further, the memory 2 may be the same as used in the apparatus described with reference to Figures 6 and 7: no special memory having a high operation speed is required, whereby the above-mentioned increased cost can be avoided. In more detail, referring to figure 8, the display apparatus embodying the invention includes, as well as the buffer memory 8, a three-state gate 7 provided in the data bus between the pattern memory 2 and the shift registers 3D and 3R. The buffer memory 8 is connected to the data bus between the gate 7 and the shift registers 3D and 3R and the horizontal address signal HAS is supplied to the buffer memory 8. The buffer memory 8 has a capacity of one line of the pattern or display memory 2, that is a capacity corresponding to one line of a pattern to be displayed. As shown in Figure 9, while the line address Ay indicated by the line address signal LAS is incremented by one at every horizontal scanning period in response to the vertical scanning position, it is not changed during the horizontal display periods Th, in contrast to Figure 6 in which it is changed between n and n' during the horizontal display periods. Further, during the even field period, the value n of the line address Ay begins to increment at a timing prior to the odd field period by one horizontal period, so that during the horizontal display period Th of the even field period, corresponding to the horizontal display period Th in which the value n is presented during the odd field period, the value is changed to (n + 1). Then, as shown in Figure 9, during the second half period Tpb of the period Tp in which Ax = m in the horizontal display period Th in which Ay = n, pattern data of address Amn (Ax = m and Ay = n) is read from the memory 2 and is written through the gate 7 to the buffer memory 8 at its address m as shown in Figure 10. Accordingly, at the end of the period Tp in which Ax = m in the horizontal display period Th in which Ay = n, as shown in Figure 10, the pattern data stored in the memory 2 for which Ay = n and Ax = 0 to m is written to addresses 0 to m of the memory 8 so that pattern data (pattern data on one line) in the memory 2 for which Ay = (n - 1) and Ax > m remains at the addresses following address (m + 1) of the memory 8. Then, at the end of the horizontal display period Th in which Ay = n, pattern data (pattern data of one line) stored in the memory 2 for Ay = n is written to the memory 8. During the odd field period, as described above, in the period Tpb of the period Tp in which Ay = n and Ax = m, pattern data is read from the address Amn (Ax = m and Ay = n) of the memory 2 and written to the address m of the memory 2. At the same time, as shown in Figure 9A, that pattern data is loaded into the shift register 3D and, during the period Tpf in the succeeding period Tp in which Ax = (m + 1), pattern data is read from the address (m + 1) of the memory 8 and loaded into the shift register 3R. In this case, while the pattern data loaded into the shift register 3D is the pattern data for Ay = n as set forth above, the pattern data loaded into the shift register 3R is the pattern data on the preceding line in which Ay = (n - 1). As a result, the display data DD is loaded into the shift register 3D, while the compared data DR is loaded into the shift register 3R. Then, the data DD and DR in the registers 3D and 3R are subjected to smoothing processing in the processing circuit 4 in similar manner to the case of Figure 7, so that a luminance signal having half dots Dh is supplied to the CRT display 5. Further, during the even field period, as shown in Figure 9B, similar processing to that performed during the odd field period is carried out. However, during the even field period, the pattern data read from the memory 2 is loaded into the shift register 3R and the pattern data read from the memory 8 is loaded into the shift register 3D. In this case, during the even field period, the line address Ay is larger by one than that during the odd field period and the value n of the even field period corresponds to the value (n + 1) of the odd field period, so that the pattern data for Ay = (n - 1) and that for Ay = n loaded into the shift registers 3D and 3R are equal to the pattern data for Ay = n and for Ay = n + 1 of the odd field period. That is, the display data DD and the compared data DR are loaded into the shift registers 3D and 3R also. Accordingly, the processing circuit 4 produces the luminance signal having the half dots Dh, which is then supplied to the CRT display 5. As mentioned above, during the period Tpb of the period Tp the pattern data is read from the pattern memory 2, while during the period Tpf the pattern data is read out from the buffer memory 8, and thus the smoothing processing is carried out. In this case, during the period Tpf of the period Tp, the memory 2 is disconnected by the gate 7 from the memory 8 and the shift registers 3D and 3R, and, during this period Tpf, the CPU 1 accesses the memory 2. As described above, since the pattern data is read out from the pattern memory 2 during the period Tpb of the period Tp and the pattern data is read out from the buffer memory 8 during the period Tpf, to thereby carry out the smoothing processing, the CPU 1 can access the memory 2 during the period Tpf, thus considerably reducing the waiting or latency time of the CPU 1. Further, the memory 2 may be the same as in Figures 6 and 7, that is a special memory having a high operation speed is not required, whereby the associated increase in cost can be avoided. The invention may be performed in other ways than that set forth above by way of example. For instance, while, in the above-described embodiment, the bit image of the pattern data stored in the memory 2 is displayed on the CRT display 5, it is possible for character codes to be written in the memory 2 as the display data and for the character codes to be fed to a character generator so as to cause display of corresponding characters, by providing a character generator on the bus line connecting the gate 7, the memory 8 and the shift registers 3D and 3R. Moreover, the smoothing processing may be carried out as follows. In any one of the field periods, the pattern data from the memory 2 is loaded into the shift register 3D and the pattern data from the memory 8 is loaded into the shift register 3R. Also, during the odd field periods, the pattern data of the shift register 3D is taken as the display data DD and the pattern data of the shift register 3R is taken as the compared data DR while, during the even field periods, the pattern data of the shift register 3D is taken as the compared data DR and the pattern data of the shift register 3R is taken as the display data DD, whereby the smoothing processing may be carried out. In addition, the format for the smoothing processing is not limited to the example shown in Figure 5.

Claims: A display apparatus comprising a display memory (2) having a capacity of a plurality of lines corresponding to effective raster scanning lines of a display, control means (6) for controlling storage of display data in the display memory (2), and a smoothing processing circuit arrangement (3D, 3R, 4) operative to carry out a smoothing processing operation based upon data of two adjacent lines read from the display memory, the apparatus being characterised in that a buffer memory (8) having a capacity of one said line is provided and in that the control means (6) is so operative that, during a first period, the display data is read from the display memory (2) and written to the buffer memory (8), while, during a second period which does not overlap with the first period, the display data is read from the buffer memory (8) and the smoothing processing is carried out by the smoothing processing circuit arrangement (3D, 3R, 4) on the basis of the display data read from the display memory (2) and the display data read from the buffer memory (8). A display apparatus according to claim 1, wherein the first period is the second half period (Tpb) of a period (Tp) corresponding to the lateral width of a character represented by one byte of the display data and the second period is the first half period (Tpf) of the period (Tp) corresponding to the lateral width of the character represented by one byte of the display data. A display apparatus according to claim 1 or claim 2, wherein the display data read from the buffer memory (8) and the display data read from the display memory (2) have a time difference of one horizontal period therebetween. A display apparatus according to claim 1, claim 2 or claim 3, which includes a central processing unit (1) operative to access the display memory (2) during the second period.

Inventors: MAEDA, SATORU, MOTOKI, KAZUO
Applicants: SONY CORPORATION
Application year: 1984
Main classification: G09G1
IPC codes: G09G5