Even I found the last post to be down in the weeds and confusing. So, here’s a better summary.

I went on an Internet dumpster dive over the weekend to find more service manuals for Yamaha keyboards. I’ve always been interested in the architecture of product families and curiosity got the best of me, again.

The Yamaha arranger keyboard family has four main tiers: 1. Premium, 2. Upper mid-range, 3. Lower mid-range and 4. Entry. These are my names. Each tier has its own hardware architecture. Let’s take it from the top.

Tyros keyboards form the premium tier. I could find service manuals for only the Tyros 2 and Tyros 3; I’ll bet that the Tyros 4 has a similar internal architecture. The Tyros has two CPUs: a main CPU to handle the user interface and peripherals (e.g., the hard disk) and a sub CPU for digital signal processing (DSP) and to manage tone generation. The main CPU bus and the sub CPU bus are connected through a bridge (implemented in gate array technology). The main and sub CPU each have their own SDRAM and program ROM. (This is true for the other tiers as well and I won’t mention it again.)

Tone generation is performed by two SWP5x integrated circuits. The SWP51 is the current series. The wave ROM is split into an upper and lower bank and is shared by the two SWP5x tone generators on a common wave memory bus. SWP51 wave ROM is dedicated to tone generation. The SWP51 implements higher waveform sample compression. Thus, the Tyros 3 actually has less physical wave ROM than the Tyros 2, even though the Tyros 3 implements memory hungry Super Articulation 2 (SA2) voices. Interestingly, there is an audio backchannel from one of the SWP51s to the hard disk subsystem. The audio data passes through an “audio transformer” circuit on its way between the SWP51 and the hard disk subsystem.

BTW, I resist making any guesses about the inner design of the new Tyros 5.

I included the Motif XS in the table for comparison. The Motif’s TX4939 is a MIPS architecture processor while the Tyros CPUs are SH-2/SH-3 architecture. (Completely incompatible, of course.) The Motif XS runs Monta Vista Linux. The tone generation architecture is very similar to the Tyros: two SWP51s and two banks of wave ROM on a shared bus.

The upper mid-range keyboards have a main CPU. However, only the S9xx keyboards have auxilliary processors. The older S910 has a sub CPU (SWX02) and bridge, an arrangement which is similar to Tyros. The S910’s TMS320 (Texas Instruments DSP) implements the MP3 CODEC. The S950 does not have a sub CPU. Its main CPU, however, has a much higher clock rate and probably took over the workload performed by the S910’s sub CPU and MP3 CODEC. The S950’s SSP2 processor is a Yamaha custom IC for vocal harmony processing.

Upper mid-range keyboards use one SWP51L integrated circuit for tone generation. Wave ROM is split into two banks and is connected directly to the SWP51L. Current generation keyboards (S750 and S950) make wide use of flash memory. More than ever, product features are determined by code and content alone.

The lower mid-range keyboards have only a main CPU: an SWX02. The SWX02 has a Renesas part number and is probably an SH architecture machine. Tone generation is integrated into the SWX02. The SWX02 has a dedicated interface to the wave ROM. The S650 has only 25% of the S750’s physical wave ROM.

The entry level keyboards are, of course, the most cost and price sensitive. The entry level keyboards can also run on battery power thereby imposing further power and performance limitations. Entry level keyboards do not provide much in the way of voice-level effects. All three of the example keyboards have a single SWL01 CPU and are all clocked at 128MHz. The ROM contains both the program and waveform data. Thus, waveform data is read across the CPU memory bus along with all of the usual program/data traffic. Physical ROM size is very much smaller then even the S550/S650. The component count is very low and the circuit boards are quite simple.