NEO-PCM2

Package	QFP120
Manufacturer
First use	1999, 2002
Used on	Cartridges, ROM-Only boards

Second version of PCM which confusingly exists in two forms under the same name. V ROM demultiplexer, decryption and P ROM banking chip.

The demultiplexing logic is exactly the same as the one found in PCM.

Jumpers

The ROM and mapping configuration for a given game is set by external jumpers. There are 3 for the V ROMs (JV1 to JV3) and 4 for the P ROMs (J1 to J4). These do not appear to affect security functions.

V ROM mapping uses address bits 20 to 23. There are 4 chip select outputs.

Security

The security function of the 1999 SNK branded version only performs address descrambling on V ROMs. The Playmore version which came out in 2002 adds a data decryption layer on top, which means both are not interchangeable.

The decryption algorithm used by emulators currently isn't perfectly exact, which explains the presence of a few corrupt bytes in decrypted romsets causing minor audio glitches (Samurai Shodown V "Basara" sample).

SNK version

P ROM bank selection is done by writing the 3 lower bits of the port zone with A19 high to not affect the V ROM setting. ie. $200000 (word) or $200001 (even) with mirrors up to $2FFFFF. Metal Slug 4 for example writes words to $2FFFF0. Todo: how does the bank number map to an address.

V ROM address scrambling is only done on the 4 lower bits by selectively inverting them depending on the configuration set by the 68k CPU. Bits 4 to 23 go straight through.

This is set by first writing 7 to the port zone, the same way P bank 7 would be selected. And then writing the 3 bit configuration value with A19 low. Metal Slug 4 for example writes words on startup to the bogus addresses $200000, $208000 and $220000.

To test:

V configuration	VA3	VA2	VA1	VA0
0	invert	invert	invert	invert
1	invert	invert	normal	invert
2	normal	invert	invert	invert
3	invert	invert	normal	invert
4	invert	invert	invert	invert
5	invert	invert	normal	normal
6	invert	normal	invert	invert
7	invert	invert	normal	invert

Playmore version

Todo.

Games

Used by:

• Matrimelee (Playmore)
• Metal Slug 4 (SNK)
• Metal Slug 5 (Playmore)
• Pochi and Nyaa (SNK)
• Rage of the Dragons (SNK)
• Samurai Shodown V (Playmore)
• Samurai Shodown V Special (Playmore)
• SNK vs. Capcom - SVC Chaos (Playmore)
• The King of Fighters 2001 (SNK)
• The King of Fighters 2002 (Playmore)
• The King of Fighters 2003 (Playmore)

Pinout

OpenOffice Draw file: File:Neo-pcm2.odg

Does the Playmore version have the same pinout ?