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Reverse Engineering the Diecom Light Gun Interface for the Color Computer

History:
A software company from Canada (Diecom) produced and sold a light gun interface box. The interface allowed you to attach a Sega Phaser Model 3050 light gun to your Color Computer. They also produced two games in order to make the gun useful: Iron Forest and Medieval Madness.
In Iron Forest there is a sample of Lori Dies saying “Welcome to the Iron Forest”. I have made a recording of that sample from the MESS emulator. Lori Dies is the sister of Diecom’s Dave Dies. It is my understanding this devices was designed by Roland Knight.

Progress:
The interface box plugged into the right joystick and serial ports of the Color Computer. The box was powered by a 9 volt battery. The Phaser’s plug was also connected to the interface box using the normal Sega controller connector. The Phaser was not modified in any way.
The interface box is a state machine with sixteen states. To advance the state you clock the serial output line (pin 4) of the CoCo from high to low. After state 15, the device goes back to state 0. The gun’s trigger is connected directly to where the joystick’s first button would be.

Clock	State	Pin 1 (30 ohms)	Pin 1 (20 ohms)	Pin 2 (30 ohms)	Pin 2 (20 ohms)	Notes
High	0			False
Low	1			False
High	1			False
Low	2			False
High	2			False
Low	3			False
High	3			False
Low	4			False
High	4			False
Low	5			False
High	5			False
Low	6			False
High	6			False
Low	7			False		State 7 should be entered at the start of a video frame. The 12-bit counter willl be cleared and will increment until the beam is found. As soon as the video frame is over, clock high.
High	7			False	True if beam found	If the beam is found then bits 1-8 of the 12 bit counter are loaded into the shift register.
Low	8	Data bit 1		False
High	8	Data bit 1	Data bit 9	False		Bit 9 is only avaiable here. On the next clock the 12-bit counter will be cleared. Data bits 1-8 are safetly stored in the shift register. Bits 0, 10 and 11 are not avaiable to the Color Computer
Low	9	Data bit 2		False
High	9	Data bit 2		False
Low	10	Data bit 3		False
High	10	Data bit 3		False
Low	11	Data bit 4		False
High	11	Data bit 4		False
Low	12	Data bit 5		False
High	12	Data bit 5		False
Low	13	Data bit 6		False
High	13	Data bit 6		False
Low	14	Data bit 7		False
High	14	Data bit 7		False
Low	15	Data bit 8		True
High	15	Data bit 8		True
Low	0			False

Hardware:

Here is a better close-up picture of the front. Here is a better close-up picture of the back. Printed Circuit Board Layouts: PCB PDF: PCB PDF with parts listed: Code Part Description IC1 CD74HC4040E 12 bit async binary counter IC2 CD74HC74E Dual flip flop IC3 CD74HC161E 4 bit binary counter IC4 CD74HC165E 8 bit shift register IC5 CD74HC00E Quad 2 input NAND gate IC6 CD74HC00E Quad 2 input NAND gate R1 20 K ohm (5%) Resistors R2 10 K ohm (5%) R3 20 K ohm (5%) R4 20 K ohm (5%) R5 20 K ohm (5%) R6 10 K ohm (5%) R7 20 K ohm (5%) R8 20 K ohm (5%) R9 5.1 K ohm (5%) R10 10 K ohm (5%) R11 5.1 K ohm (5%) R12 100 K ohm (5%) C1 10 nano-farads Capacitors C2 10 nano-farads C3 10 nano-farads C4 0.18 nano-farads C5 0.1 nano-farads Q1 78L05 ACP Motorola 652 Voltage Regulator Q2 735 2N3904 (NPN) NPN General Purpose Amplifier and Switch D1 (Diode) no markings CO1 FOX143 14.31818 Crystal Misc. 9v Battery Connector 6 pin DIN plug (CoCo Joystick) 4 pin DIN plug (CoCo Serial) 9 pin plug (Light Gun) Schematic (preliminary):