Acer AL2002 AL2002 Service Guide - Page 8

7 Go to cover page 3.4.2. Video Signal Amplitudes The three video inputs consist of Red, Green, and Blue signals, each with its own coaxial cable terminated at the monitor. These video signals are analog levels, where 0V corresponds to black, and 735 mV is the maximum signal amplitude for the respective color, when each signal is terminated by a nominal 75.0 ohm. For a given monitor luminance levels are measured using this defined video amplitude driving a monitor meeting the termination requirements. The signal amplitude is not to be readjusted to compensate for variations in termination impedance. 3.4.3. Video Signal Termination Impedance This analog video signal termination shall be 75 ohm +/- 2% which shall be resistive with a negligible reactive component. 3.4.4. Synchronization (Sync) Signals The Horizontal Sync (HS) TTL signal is used to initiate the display of a horizontal line. HS may be either active high or active low, depending upon the timing. The Vertical Sync (VS) TTL signal is used to initiate the display of a new frame. VS may be either active high or active low, depending on the timing. 3.4.5. Sync Signal Levels The monitor must accept sync signals from both 3.3 and 5 volt TTL logic families. The inputs shall sense a logic 0 when the input is 0.8 volt or less and shall sense a logic 1 when the input is 2.0 volts or greater. In addition to these level requirements, there shall also be a minimum of 0.3 volt hysteresis provided for noise immunity (typically by using a Schmitt Trigger input). That is, the input level at which the monitor actually detects a logic 0 shall be at least 0.3 volt lower than the level at which it actually detects a logic 1. If the monitor sync processing circuits are designed around the 3.3 volt logic family, then the sync inputs must be 5 volt tolerant. 3.4.6. Sync Signal Loading TTL input loading shall be equivalent to one TTL input load. When logic 0 is asserted by a sync input, the maximum current source from any single monitor sync input to the driver is 1.6 mA. When logic 1 is asserted, the maximum current source from the driver to any single monitor sync input is 400mA. 3.4.7. Abnormal Signal Immunity The monitor shall not be damaged by improper sync timing, pulse duration, or absence of sync, or abnormal input signal amplitude (video and/ or sync too large or too small), or any other anomalous behavior of a graphics card video generator when changing modes, or when any combination of input signals is removed or replaced. Additionally, under these conditions, the monitor shall not cause damage to the driving source.