gnome@olivee.UUCP (Gary Traveis) (04/27/84)
Some people with 3D cartridges were wondering how the imager acts when plugged in. Well here goes... Here is what I found when scoping out the Vectrex 3D imager pins. First off, there are only four pins used - Pin# what 7 +5vdc 8 GND 4 Index hole (from imager) 3 Pulse out (from system) This is what I saw --- On startup the program sends a "high torque" sequence consisting of a high freqency pulse train -- 1 ----- (160us) --------------------- (160us) ---------- 0 _________ (520us) _________ <PIN 3> This frequency is sent out until the wheel gets up to speed, which is sensed by index pulses sent from the imager to the system. When the wheel reaches the correct 23rps (rev's per Sec), the system backs down the pulse frequency to the following -- 1 -------- (2ms) -------------------------- (2ms) ----------- 0 ________ (40ms) ________ <PIN 4> 1 ---------------- (2/20ms) ----------------------- (same) --- 0 ______............... ________....<PIN 3> The Vectrex is then acting as a software phase-locked-loop. As the wheel slows slightly, the timing loop (or interrupt?) detects a longer pulse-to-pulse time and boosts the wheel speed by sending one or two 20ms pulses to the motor control input (pin 3). The index pulse is sent at the time just before the left eye is "opened" or entering the red-green-blue sequence. It also is the "closing" time for the right eye. Even though I haven't tried to simulate the index pulse yet, in order to run a 3D program without the imager, I intend to see just how picky the program is. Unfortunately, wiring pin 3 to pin 4 doesn't work because the "high torque" sequence never satisfies the criteria for being "up to speed", never terminates, and the screen stays blank. I hope to follow up with an index simulation circuit as soon as my spare time reaches the critical level to get myself into gear... More to come... Gary (hplabs,fortune,allegra)oliveb!olivee!gnome(@BERKELEY.ARPA)