J-r programmer v2 switches

Atari Games I worked on several XY games. This article represents what I know about J-r programmer v2 switches Generators.

This is the companion piece to The Secret Life of XY Monitors. The Digital Vector Generator was the first vector generator Atari developed, and was used in Lunar Lander, Asteroids, and Asteroids Deluxe. First, notice that the DAC’s most significant bit is ‘B1’ and that the order of the bits is backwards from what we normally see. Texas Instruments persisted in labeling their EPROM data as ‘d1’ – ‘d8’ long after others adopted the current standard. Even today the world is divided into two warring factions when it comes to how to order the bytes in a word. Intel Camp uses the Low Byte, High Byte order. Not only does it matter in microprocessors, it can matter when two computers are exchanging data.

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The classic article on the subject is On Holy Wars and a Plea For Peace by Danny Cohen, written in 1980. In this example we are assuming a voltage output which represents the position of the beam on the screen of the XY monitor. What we want is to have 0 in the middle of the screen, with positive numbers to the right and negative numbers to the left. 2 to the output of the DAC.

With a 10-bit number in Two’s Complement Form the most significant bit is the sign bit. Two’s Complement Form is exactly what we want. Numbers in Two’s Complement Form are the easiest to manipulate in binary arithmetic. 512, which produces a VOUT of -1 step. Now that we have gotten that out of the way, let’s do some digital stuff. Let’s connect a counter to the DAC as shown in Figure 4.

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