Re: RCX sound circuit

Hello Mark,

> Your circuit diagram checks out Philo, though a 47k resistor to ground should 
> be
> added to the processor connection.  

Quite possible as I obtained the schematics only with an ohmeter...

>
> I was wondering what the other NAND gate is used for.  Input pin 1 traces to
> somewhere under the ROM.  Input pins 2 and 13 and output pin 12 disappear
> elsewhere.
>
I spent some time again with my ohmeter, here is the schematics for this part:
http://www.brickshelf.com/gallery/Philo/RCX-comp/motor_cmd.gif

This is the motor driver control circuitry, data is latched when there is a
write to address x111 xxxx xxxx xxxx (binary). As I think H8 is used in mode 2,
A15 is always 1 for external access, so any write to fxxx should write to motor
driver latches. In the schematics, OUT_X_1 and OUT_X_2 are connected to Melexis
motor drivers in1 and in2.

> I suggest that a 3-input NAND gate was needed by the main computer circuit and
> that the speaker driver circuit just mopped up the spare gates.
Probably, yes ;o)

Philo