| 摘要 |
PURPOSE:To improve an address indicating accuracy by a light pen, by varying an amplification factor of a bright line detecting signal detected by the light pen, and limiting the number of binary-coded bright line signals to several pulses. CONSTITUTION:In case a luminance of a CRT1 is varied, sometimes the number of pulses of a binary-coded bright line signal (d) is varied from an initial set value, and sometimes an address indicating accuracy is deteriorated by a light pen 2. According to this device, it is settled by monitoring the pulse of the binary-coded bright line signal (d), and adding an amplification factor setting circuit 21 for verying an amplification factor of a variable amplifying circuit 3 by the number of said pulse. That is to say, the address indicating accuracy by the light pen 2 is improved by monitoring the number of pulses of the binary-coded bright line signal (d), decreasing the amplification if its number in the second field is above the first set value, and on the contrary, increasing it if said number is below the second set value.
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