Speak & Spell


I bought a couple of broken Speak & Spells off ebay and munged together one working unit. I desoldered the chips from the broken PCB and with the datasheet provided to me by Lord Nightmare, dumped the ROM contents. There are two ROM chips (Voice Synthesis Memories, or VSMs) on the PCB, and one of the S&S units came with the module Vowel Power. The VSMs are serial ROMs with their own built-in address counters. They are similar to but not as advanced as Fairchild PSUs; an address is loaded, then bits are clocked out one at a time starting at that address. Each VSM holds 16K, and the internal address counter is 18 bits long, so 16 of them can be on the same bus, as long as they are set up for different 16K banks. The 2 VSMs on the main PCB are TMC0351NL and TMC0352NL. The VSM in Vowel Power is TMC0350NL CD2302. Here's a picture with the top metal layer removed.

My dumping circuit is pretty simple; I connected 3 outputs of a PIC processor to a CD4504 CMOS level translator to send clock and control signals to the VSM. I tied the address lines to ground with 10K resistors so that the address would be loaded with 00000. I connected a 22K resistor from ADD8 to a PIC input to read the data bits. Then I clocked out 2097152 bits, packed each 8 bits into a byte, and dumped those 262,144 bytes to the serial port.

The '351 VSM is programmed at bank 0, 0000-3FFF. '352 is bank 1, 4000-7FFF and '350 is bank 2, 8000-BFFF. Bits out of those ranges are dumped as 0s. My code takes 54 seconds to dump all 262,144 bytes. Here's a screengrab of the signals from a Saleae Logic16 showing initialization, address loading, and reading the first 2 bytes from '351, which are dumped LSB first, making them 33 33.

There are 2 other chips on the printed circuit board: TMC0271NL and TMC0281NL. The '271 is similar to a TMS0980, a microcontroller with RAM, ROM and I/O, while the '281 is specially designed for speech synthesis. I decapped one of each- unfortunately, the '271 die got stuck in the plastic, and I damaged it while getting it unstuck. Here's a picture of it. The '281 turned out much better; here's a quick composite from ICE.


Here's a later revision of the '271 labeled TMC0271H-N2L FDS 8149:

with top metal

top metal removed

raw ROM dump


CD2704B-N2L DFW 8231 is an MCU used in Speak and Math:

with top metal

top metal removed

raw ROM dump


CD2702A N2L QFW 8432 is an MCU used in foreign language Speak & Spells:

with top metal

top metal removed

ROM array with top metal

ROM array top metal removed

raw ROM dump


Speak & Spell info from Datamath

Speak & Spell history


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