Texas Instruments Touch & Tell

Found at a swapmeet, did not work when I got it.

So I reverse engineered the power supply.

The red dot is pin 1 on the solder side. I arbitrarily numbered the pins clockwise from there.

I also removed the transformer to check -- pins 2, 7 and 8 are not connected to anything inside the transformer, and are only connected on the PCB because they are in the way.

It has some similarity to the Speak & Spell power supply, but I suppose that's inevitable.

Note on pins 1 (POWERDOWN) and 2 (STARTUP) -- To turn the unit on, a keypress pulls pin 2 high, and powers up the unit. The processor then pulls pin 1 high to keep the unit on, until it decides to power down, when it pulls pin 1 low. More at furrtek.

Pin 1 goes to the CD8012 pin 2, and pin 2 goes to the keyboard connector pin 2 (Thom's numbering) and to the CD8012 pin 6.

Turning Q3 on biases Q1, which will oscillate because of the feedback from the transformer. Enough (negative) voltage at the output (determined by the zener) will start turning Q2 on which removes some of the bias voltage, thereby regulating the output voltage.

Pin 4 is connected to the CD8012 / TMS1100 pin 9, which functions as some kind of a reset I think, I don't know the TMS1100 at all.

The zener has a thick grey band and two red bands, so it might be an 8.2V zener -- I measured 8.46V (at 75uA) when the circuit is working -- and yes, the power supply is in fact working, and probably good for around 50mA -- at 90mA the output drops from 9.4V (between Vss / Batt + and Vdd / output) to 9.1V.

So why does the unit not power up? Turns out most of the keys on the keyboard are shorted, if I disconnect the keyboard and poke the connector with a wire, it works.

Keyboard

This is a 4 x 9 matrix. Note that 3 & 8 is not a connection, but 2 & 14 (VSS) is. The 3 & 8 input is used on the 5-way select switch.

The TMS1100 has four inputs (K1 K2 K4 and K8), eight independent outputs (R0 to R7) and eight decoded outputs (O0 to O8) where a 4-bit value is mapped to the eight outputs via the mask ROM, so it can be one-of-eight or seven-segment or whatever. But the eight outputs can only have 16 + 4 different states. Read the manual. It's complex.

Schematic

(See also Finding the hidden Speak & Spell in a Renault 25)

CD8012 : 4-bit TMS1100 microcontroller with 2k Bytes ROM and 128*4 Bits RAM
CD2802 : TMS5110A VSP (Voice Synthesis Processor)
CD2610 : VSM (Voice Synthesis Memory) with 16k Bits capacity

The VSP generates a clock at 640kHz and feeds it (divided to 320kHz)to the CPU. While the 4-bit control interface is bidirectional, in this implementation the CPU writes four bits to the VSP, but only reads one bit (CTL1) via the two-diode MUX (obviously at a time when there is no keyboard scan activity).

• The strange, cartridge-powered speech of TI Touch & Tell
• Thom's Bend
• ROM dump
• Datamath Touch & Tell
• Datamath Vocaid
• Speak & Spell schematic