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Fast Position Controller for a Directed Beam Display

IP.com Disclosure Number: IPCOM000047480D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Evans, PJ: AUTHOR

Abstract

The Fast Position Controller behaves as an up/down counter driving a digital-to-analog converter. The output is then used to drive the X or Y inputs of a directed beam display, such as the IBM 3251. The effective beam writing speed is limited by the maximum count rate, together with the need for high resolution, in order to minimize &staircase& effects. Using a conventional counter, running at about 25 megahertz, would result in a limiting beam writing rate of 75,000 inches/second for a 12" x 12" picture with 4K resolution. Using the counter described in this article the maximum beam writing speed can be extended to 1,000,000 inches/second at a comparatively modest clock rate of 21.33 megahertz.

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Fast Position Controller for a Directed Beam Display

The Fast Position Controller behaves as an up/down counter driving a digital-to- analog converter. The output is then used to drive the X or Y inputs of a directed beam display, such as the IBM 3251. The effective beam writing speed is limited by the maximum count rate, together with the need for high resolution, in order to minimize &staircase& effects. Using a conventional counter, running at about 25 megahertz, would result in a limiting beam writing rate of 75,000 inches/second for a 12" x 12" picture with 4K resolution. Using the counter described in this article the maximum beam writing speed can be extended to 1,000,000 inches/second at a comparatively modest clock rate of 21.33 megahertz. This is achieved by enabling the counter to increment or decrement at rates of up to 16 per clock pulse, under the control of a 16-bit rate select field. The bandwidth of the X and Y deflection systems is typically 4 to 10 megahertz, and therefore cannot distinguish between this counter and one counting at the same rate, but normally at 16 times the clock frequency. Referring to the figure blocks 'B' through 'G' form a 12-bit, up/down counter/register, which drives a digital-to- analog converter 'A'. The output of 'A' is used to drive the X or Y inputs of a directed beam graphic display, such as the IBM 3251. Blocks 'F' and 'G' provide the 8 most significant bits of the system, and consist of two synchronous counters, cascaded in the normal way. Blocks 'B' through 'E' are the output latches providing the least significant 4 bits of the system. These latches, together with blocks 'H', 'J', and 'K' form a special up/down synchronous counter. It is spec...