ZVG
Features and
Specifications

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Description & Features

The ZVG is an Analog Vector Generator and therefore there are no stair stepping effects. All vectors are drawn as a smooth continuous lines between endpoints. The vector generation logic allows direct addressing of vector endpoints, and unlike the Atari's AVG, there is no vector drift.

Connecting the ZVG to an ECP capable parallel port allows the PC to directly drive both B&W and Color X/Y monitors, including the B&W monitor used by the portable Vectrex gaming platform. The ZVG hardware is capable of 1200x1200 endpoint resolution, but is driver limited to 1200x944 to prevent monitor stress.

By using an analog vector generator that allows direct endpoint addressing, the ZVG uses the best of both worlds when comparing a Digital Vector Generator and an Analog Vector Generator. It uses an Analog Vector Generator for smooth continuous vectors, and yet still allows direct addressing of the endpoints, like that of a Digital Vector Generator. This allows the ZVG to emu late all known Vector Generators, which include the Digital Vector Generators such as Atari's earlier B&W games, the Sega games, and the Analog Vector Generator used by Cinematronics (that also allowed direct positioning of the vector starting point). It can also emulate relative addressed vector generators, like the analog vector generators used by Atari.

1200x1200 Resolution
The ZVG allows 1200x1200 addressable endpoints. This is the hardware resolution, and is driver limited to 1200x944, to prevent monitor stress.

To take into account the 4:3 viewing ratio of a standard monitor, and to give games the ability to overscan the monitor's edges, the ZVG is setup to use a viewable area of 1024x768 endpoints, with the ability to overscan the borders to 1200x944 endpoints. Vectors that are drawn beyond the 1024x768 window will extend beyond the edges of the monitor. A 1200x944 overscan boundary allows vectors to be drawn 1.23" off the edge of a 19" monitor. Overscanning was mostly used by Atari in games like Tempest. Tempest placed no limits on the amount of overscanning, whereas by limiting overscanning to 1.23", the ZVG achieves the same visual effects without generating the possibly monitor damaging voltages that Tempest is known for.

Full Range of X / Y Drive Voltages
The ZVG X and Y full range capabilities are +12 / -12 volts. Through jumpers and adjustment pots the X and Y drive voltages can be set to drive any Arcade X / Y monitor. Also included are adjustments for centering X and Y offsets.

65536 Colors or 64 Levels of Grayscale
The ZVG uses a 16 bit color depth. Five bits are used for Red and Blue, six bits are allocated for Green for a total of 65536 colors. When driving a B&W monitor, the Green output is used as the Z-signal for a total of 64 levels of grayscale. These values far exceed the specifications of the monitors being driven, allowing for full use of the monitors' capabilities.

Selectable Drawing Speeds
Drawing speeds are jumper selectable and based on the speed of vector movement on a 19" monitor. Vector draw speed is constant, so vector movement will be faster on larger monitors, and slower on smaller, but the time it takes to draw the vector will remain constant. There are four selectable speeds: 15us / 30us / 40us / 50us per inch.

Built in Pincushion and Edge Bloom correction
To properly drive the WG 6100 series monitors, both Pincushion and Edge Bloom correction must be used. The ZVG has jumpers to enable / disable these features.

Adjustable Endpoint Intensities
Software adjustable endpoint intensities allow compensating for different yoke speeds and allow adjusting the "look" of a vector to taste. Some prefer bright points at the ends of vectors, some prefer constant intensity vectors.

Adjustable Relative Point Intensities
The ZVG firmware allows adjusting of the intensity of a point relative to the intensity of a vector. Once vector endpoints have been set to taste, the point intensities can be adjusted to match.

Adjustable Between Vector Jump Speeds
For increased efficiency, the speed at which the CRT trace "jumps" between the endpoint of one vector and the start of the next can be set higher than the speed at which a vector can be drawn. Any non-linearities in trace movement, caused by the higher jump speed, will not be seen since the trace is blanked. The "between vector jump speed" is software adjustable.

Adjustable Color and Grayscale Voltage Settings
The minimum and maximum allowable DAC voltages values are under software control. This allows setting the proper voltages needed for full contrast and brightness for any vector monitor. Most Arcade Game Vector monitors required similar Z-axis voltages, however monitors such as the Vectrex vector monitor, require non-standard Z-axis voltages, which can be accommodated.

All Firmware Settings Backed up in EEPROM
All setup parameters that are not jumper selectable are save in EEPROM. This includes such things as control of the timings used to draw a vector, and the DAC voltages used to generate colors and gray scales. The settings of the these values are done using the software utility ZvgTweak. Once setup, the values may be stored in EEPROM. Separate values are kept for each of the four different monitor speeds supported by the ZVG.

Monitor Safety was a Design Priority!
Arcade style X/Y Monitors have not been manufactured for at least 20 years, they are not easy to come by, and are not cheap. Every effort has been made to protect the X/Y monitor under normal use, and under adverse conditions. Here's a list of monitor safety features implemented in the ZVG:

• Safe Power On. Immediately upon power on, or reset, all outputs are set to a "monitor safe mode" and remain there until all power on self tests are completed without error. The monitor safe mode is indicated by 0.0V on X, Y and Z outputs (no Z-drive, the CRT trace held at center position).
• Power On Self Tests (POST). All EPROMs are checksummed tested, communications between the two onboard processors are verified, EEPROM state values are checksummed, and ranged tested before being accepted as valid.
• Brown out detection. Any unsafe voltage fluctuations on the power supply will cause the ZVG to go into the monitor safe mode.
• Watchdog timers on both processors. If, for whatever reasons, either of the ZVG processors lock up, a watchdog timer will kick in and reset the ZVG into the monitor safe mode.
• Vector Activity Timeout. If no vector activity is present on the parallel port for more than 250ms, the ZVG will immediately enter the monitor safe mode. This can occur if the parallel port connector is removed or jarred lose, or the PC locks up or is turned off, or the PC software crashes, etc. This prevents the CRT trace from being held in a non-centered position for any length of time, which can cause a vector monitor to overheat. It also helps guard against burn in, in the case of a defective spotkiller, since the monitor safe mode also turns off the Z-drive.

Upgradeable Firmware
Should the need arise, the ZVG's firmware is fully user upgradeable.