
>From the Vectrex Technical Description (my comments in {curly braces}):

The HP3000 {Vectrex} is a microprocessor based, vector scan system using a
standard 9" black & white CRT as its video display device. The
microprocessor (MPU) is the Motorola 68A09 device {hardware multiply and
divide!}. The MPU operates at 1.6 MHz from a 6 MHz extrenal Xtal. An
internal divide by 4 circuit generates the MPU 1.6 MHz "E" clock signal used
in the system. Program memory is stored in the 8K x 8 2363 {really 2764}
type ROM. This ROM contains common subroutines, the "executive" or assembler
instructions plus one complete game {Mine Storm}.

Two 1K x 4 2114 type static RAMS provide storage locations for data
indicative of locations of objects, game status, and various other
information needed by the microprocessor during game operation. Peripheral
Interface Adaptor (PIA) Chip {a 6522A}, has two 8 bit peripheral ports which
interfaces the MPU with peripheral devices and external signals. One of the
PIA ports interfaces the General Instruments AY-3-8912 sound-IO chip with
the MPU and also drives the digital to analog converter chip MC1408. The
other PIA port is used as control lines for the sound chip, selector control
for the multiplex chip and as means to read the A/D comparator that's used
in the joystick successive approximation circuitry. Sound is either MPU
generated directly or by use of the AY-3-8912 sound chip.

The AY-3-8912 sound chip is a programmable sound generator containing 3 tone
generators and wave shapping circuitry. This chip also has a single 8 bit IO
port used to read the status of each of the handcontrollers 4 action
switches.

The standard TTL device types 74LS00 and 74LS32 are usued as control line
decoders to allow the MPU to select the appropriate circuit element to be
addressed at any particular time.

The analog processing section includes digital to analog converter (DAC)
chip type MC1408, dual 4 channel multiplexer/demultiplexer chip type CD4052,
and dual op-amps types LF353 and LF347.

DAC chip M1408 receives an 8 bit word at data terminals D0-D7. DAC output
(pin 4) is current source. One section of IC LF353 is used to change this
current to a voltage representative of the 8 bit digital word received by
the DAC chip. The LF353 voltage is applied to an input of the dual 4 channel
multiplexer (MUX) chip CD4052. This same voltage (designated "DAC" on the
schematic) is the X-axis drive signal.

The CD4052 MUX chip serves two purposes: it selectively couples, under MPU
control, the output of the DAC current/voltage converter to one of 4 places
and is used to selectively couple the inputs from the joystick pots to the
voltage comparator IC LF353.

The 4 places to which the "DAC" signal is coupled by the MUX are:

1) The Y-axis sample and hold IC LF347
2) The "0" reference charge capacitor
3) The Z-axis (brightness signal) sample and hold IC LF347
4) MPU sound resistive netowrk

Each of these 4 signals is a voltage value representative of the 8 bit DAC
input word for that function.

The joystick pot positions are sensed by a successive approximation process.
The MUX chip selects each joystick pot input line and applies it to the plus
input of comparator IC LF353. At the same time the MPU generates digital
words that are changed to voltages by the DAC and current/voltage converter
mentioned previously. These voltages are successfully {successively} applied
to the comparator's minus input until the MPU generated voltage is equal to
the joystick voltage. The MPU then recognizes the digital word
representative of the comparison voltage and is able to establish a location
for the joystick pot. The present position for each joystick is sensed in
this manner. The pot position information is updated on a regular basis by
the MPU.

Returning to the X and Y axis drive signals, these signals are applied to
X,Y integrator IC LF347 negative input pins through series analog switch
types 4066B. The "zero" reference signal is applied to the positive inputs
of the integrators. There are also analog switches across integrator IC
capacitors. The series analog switches are controlled by MPU signal RAMP and
the parallel capacitor switches are controlled by MPU signal Zero 10. RAMP
10 determines when and for how long the X and Y axis voltage levels will be
applied to the integrator amps. Zero 10 is used to discharge the X & Y axis
integrator caps thus initializing them for the next signal to be integrated.

The outputs of the X,Y axis integrators are coupled through J-FET switches
to IC LM379 deflection amplifiers. The LM379 operates as a voltage to
current driver, the current through the deflection coils forming the
electromagnetic field which deflects the CRT beam. To protect the CRT from
spot burn in the event of a loss of deflection, the Y axis drive amplifiers
output is detected and a deflection enable/disable signal is generated. This
signal controls the J-FET switches in series with the X,Y deflection amp
inputs to reduce the scan drive signal in the event of a software or
hardware failure plus discrete transistor type 2SC1921 operates to bias off
the CRT.

Conventional full wave rectification and three terminal regulators are used
in the low voltage power supply. A special negative DC source is generated
by a voltage double-circuit which is used to supply a 13V to the DAV chip.

The high voltage is generated via an oscillator, drive transistor and
flyback type transformer circuitry similar to what is commonly used in small
black and white TV receivecrs.

Judicious use of bypass caps, RF filter chokes, ferrite beads, etc., has
been used in the design to control RFI emmisions.
--------------------

{Me again}
The cartridge connector has the following lines from the MPU: A0-A15, D0-D7,
R/~W, ~HALT, ~NMI, ~IRQ, ~E, a cartridge chip select, and one bit from PIA
port B (PB6).

I've dumped the contents of the Exec ROM in to a file... One of these days
somebody will get around to disassembling it... (any volunteers?)

If you'd like copies of the schematics and block diagrams, drop me your
snail address.

There's a bunch of us here at CMU interested in hacking on our Vectrexes
(Vectrex-People@CMUC). If we come up with anything good, I'll let the net
know. If anybody out there has come up with anything, or wants to get
involved, let me know... We could have a world wide effort!

                cheers, -m-





