Adding the CM-32L's functions to a rev. 1 MT-32

[Great Hierophant]

Research on this forum has shown that it is technically possible to add the extra capabilities of the CM-32L (the extra 33 sound effects) to the MT-32, rev. 1.  We know that the CM-32L and the rev. 1 MT-32 sound and function identically except for this feature.  We also know that the LCD screen, buttons and rotary dial of the MT-32 will function with the CM-32L's Control ROM.  Someone on this forum proved it last year. 

The only question that remains is how to add the extra sample ROM?  The MT-32 has its sample banks in 2 x 256KB ROMS, the CM-32L in 2 x 512KB ROMs.  This schematic gives the pinouts for the ROMs as the connect to the LA chip.

http://s-island.mixnmojo.com/stuff/5.jpg

From here we can probably guess how the MT-32's addressing works.  It is almost certainly exactly like this except that there is no A18 to connect on the smaller ROMs. 

So, what do we do with this information?  Well, we disconnect the soldered sample ROMs inside the MT-32, get a pair of 512K EPROMs, flash them with the CM-32L code, then solder them (standard EPROM using the same pinout as the Roland ROMs) in and wire A18 to LA60. 

The second step is to remove or reflash the MT-32's ROM/EPROM with the CM-32L's code. 

If this works, then you get the benefits of the CM-32L with the advantages of the MT-32! 
This assumes the multiplexing of the ROMs is the same in the rev. 1 MT-32 as in the CM-32L except for the difference in ROM sizes. 

[Cloudschatze]

The 01 MT-32 has a single, 4Mbit PCM ROM
The CM-32L has two, 4Mbit PCM ROMs

Didn't we cover this stuff a year-and-a-half ago? I must have been the only one who liked Laust's idea... 

[Great Hierophant]

We mostly did, but never quite figured out how connecting the ROMs would go.  Now we know, all we need to do is to add a single 4Mbit ROM, (piggybacked to the original rom), and enable the multiplexing as it is done on the CM-64 schematic (i.e. with a 74HC02.) 

[Great Hierophant]

Actually, based on the schematic, you could simplify the modification further.  Since LA59 seems to be the equilavent of A19, so get an 8Mbit ROM, combine the MT-32 + CM-32L ROM code together, and burn it to the one ROM.  Then replace the PCM ROM on the MT-32 and wire EPROM A19 to LA59.  This is based on my analysis of how the multiplexing seems to work. 

The schematic is somewhat ambiguous about what IC8 is supposed to be.  Its symbol seems to indicate a NAND gate, but an HC02 contains only NOR gates.  In the end, as it is wired it does not matter since the end result would be the same regardless.