Browse Prior Art Database

Logic Equivalent of Analog Flywheel Sync Circuit

IP.com Disclosure Number: IPCOM000043313D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Peel, RS: AUTHOR

Abstract

This article relates to controlling an IBM 3279 display by an IBM Personal Computer (PC). The circuit described provides an uninterruptible sequence of horizontal sync (HR) pulses to the analog sync circuit while the PC HR changes very rapidly under program control. Also the circuit generates convergence logic clocks from the PC clock and allows change from PC to 3279 under program control. The figure is a block diagram of a logic interface between an IBM PC and an IBM 3279 display. The incoming PC clock PC1 is divided by 3 to produce a clock PC2, almost equal to the 3279 character clock. PC2 clock runs a counter which can count either 101 or 102 characters. The output of this counter and the PC2 circuit is used to reproduce the various clocks and syncs required for the convergence and analog circuits in the 3279.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 2

Logic Equivalent of Analog Flywheel Sync Circuit

This article relates to controlling an IBM 3279 display by an IBM Personal Computer (PC). The circuit described provides an uninterruptible sequence of horizontal sync (HR) pulses to the analog sync circuit while the PC HR changes very rapidly under program control. Also the circuit generates convergence logic clocks from the PC clock and allows change from PC to 3279 under program control. The figure is a block diagram of a logic interface between an IBM PC and an IBM 3279 display. The incoming PC clock PC1 is divided by 3 to produce a clock PC2, almost equal to the 3279 character clock. PC2 clock runs a counter which can count either 101 or 102 characters. The output of this counter and the PC2 circuit is used to reproduce the various clocks and syncs required for the convergence and analog circuits in the 3279. Without an incoming horizontal sync from the PC (PCHR), this circuit free runs at 102 characters. If the lead ing edge of the PCHR occurs during character 101, then the counters are reset such that it cycles at 101 1/3 characters and remains locked to the PCHR. Any change in the PCHR frequency will result in this circuit going back to a cycle time of 102 characters. When the HR output of the character clock is coincident with the 3279 HR, then the mode can be changed to or from PC mode. This operation guarantees that the HR to analog cannot change in frequency by more than 1% or be interrupted in any way....