Replacement chip

Dirty page for SNK chips replacements development.

Reading various [repair logs], it appears that dead or partially dead SNK chips are a common issue. It forces cannibalism and forcibly reduces the worldwide stock.

For preservation, it would be desirable to produce drop-in replacement chips to save original boards.

Considered solutions

Nobody likes rewiring to accomodate different pinouts, especially 80+ pins chips. Producing new ASICs is out of the question because of the price at low quantities, and because finding pin-compatible models todays would be difficult if not impossible.

The only solution would be adapter boards the size of the original chips, with castellated vias for surface mounting ? Furrtek (talk) 18:41, 15 January 2016 (CET)

• Reconstruct the chip's logic with regular logic chips ? No: they're all too big. BGA parts aren't 5V compatible.
• Use 2 boards on top of each other with a mezzanine connector ? No, no, no.
• Use 1- or 2-gate SOT-23-5/6 chips ? Maybe in some cases, but would be expensive (long BOM, lots of parts to assemble).
• Use a CPLD ? Probably the best solution. Altera's MAX3000 and Xilinx's XC9500 are 5V-tolerant and are still available at reasonable prices.

CPLD proposals

• NEO-257: 53 I/Os, EPM3064 in TQFP100 ?
• NEO-273: Only used in cartridges, rarely dies. A clone wouldn't be that useful ?
• NEO-BUF: Really a pain, too small for QFP CPLDs. 74LVCH16245 in BGA56 ?
• PRO-C0: Need pinout, quite big so EPM3128 in TQFP144 ?
• NEO-C1: EPM3128 has enough I/Os, but too big in TQFP144.
• NEO-D0: 55 I/Os, EPM3064 in TQFP100 ?
• NEO-E0: 54 I/Os, EPM3064 in TQFP100 ?
• NEO-F0: 60 I/Os, EPM3064 in TQFP100 ?
• NEO-G0: 56 I/Os, EPM3064 in TQFP100 ?
• NEO-I0: 56 I/Os, EPM3064 in TQFP100 ?
• NEO-ZMC: Very small, can be found on AliExpress (January 2016). BGA ?
• NEO-ZMC2: 71 I/Os, EPM3128 in TQFP100 ?
• PCM: Only used in cartridges, rarely dies. 65 I/Os, EPM3064 in TQFP100 ?
• NEO-DCR-T, NEO-SDR-T: Need pinouts, probably same problem as for NEO-C1.

• LSPCs could be replaced but the I/O requirements directs to >$60 CPLDs.
• Line buffers (PRO-B0, NEO-B1) could be replaced with MAX10's and level shifting ?. Might be too expensive.

Board proposals

Which board houses are castellation friendly ? Is classic 1.6mm good ?

Logic definitions

Use pin names instead of numbers ?

NEO-257

Verified: NO.

// TODO: Reverse order of bits/pins
assign {8,9,11,12,23,24,27,28} = (35&~18) ? 17 ? {5,7,14,16,20,22,30,32} : {4,6,13,15,19,21,29,31} : 8'bzzzzzzzz;
assign {40,41,43,44,55,56,59,60} = (35&(~(33|34))) ? 17 ? {36,38,45,47,51,53,62,64} : {37,39,46,48,52,54,63,1} : 8'bzzzzzzzz;

NEO-273

Verified: NO.

reg [19:0] C_LATCH;
reg [15:0] S_LATCH;

assign {46,45,44,43,41,40,39,38,14,13,12,11,9,8,7,6,33,32,1,64} = C_LATCH;
assign {37,36,35,34,18,17,16,15,5,4,3,2,51,50,49,48} = S_LATCH;
assign 47 = ~46;

always @(posedge 23)
  C_LATCH = {27,25,59,57,55,54,53,52,31,30,29,28,22,21,20,19,63,62,61,60};

always @(posedge 24)
  S_LATCH = {55,54,53,52,31,30,29,28,22,21,20,19,63,62,61,60};

NEO-BUF

Verified: NO.

// A0~7 <= B0~7
assign {32,33,34,35,37,38,39,40} = (44|45) ? 8'bzzzzzzzz : {5,4,3,2,1,48,47,46};
// A8~15 <= B8~15
assign {22,23,24,26,27,28,29,30} = (44|45) ? 8'bzzzzzzzz : {16,15,14,13,10,9,8,7};
// B0~7 <= A0~7
assign {5,4,3,2,1,48,47,46} = (44|(~45)) ? 8'bzzzzzzzz : {32,33,34,35,37,38,39,40};
// B8~15 <= A8~15
assign {16,15,14,13,10,9,8,7} = (44|(~45)) ? 8'bzzzzzzzz : {22,23,24,26,27,28,29,30};

NEO-C1

Verified: Absolutely not.

// Address decoding
assign ROMZONE = |{A23I,A22I,A21,A20};                   // 000000 0FFFFF
assign WRAMZONE = |{A23I,A22I,A21,~A20};                 // 100000 1FFFFF
assign PORTZONE = |{A23I,A22I,~A21,A20};                 // 200000 2FFFFF
assign CTRL1ZONE = |{A23I,A22I,~A21,~A20,A19,A18,A17};   // 300000 31FFFF
assign ICOMZONE = |{A23I,A22I,~A21,~A20,A19,A18,~A17};   // 320000 33FFFF
assign CTRL2ZONE = |{A23I,A22I,~A21,~A20,A19,~A18};      // 340000 37FFFF not sure if A17 is used (up to 35FFFF only ?)
assign BITW0 = |{A23I,A22I,~A21,~A20,~A19,A18,A17};      // 380000 39FFFF ?
assign BITW1 = |{A23I,A22I,~A21,~A20,~A19,A18,~A17};     // 3A0000 3BFFFF ?
assign LSPCZONE = |{A23I,A22I,~A21,~A20,~A19,~A18};      // 3C0000 3DFFFF not sure if A17 is used (up to 3DFFFF only ?)
assign PAL = |{A23I,~A22I};                              // 400000 7FFFFF
assign CARDZONE = |{~A23I,A22I};                         // 800000 BFFFFF
assign SROMZONE = |{~A23I,~A22I,A21,A20};                // C00000 CFFFFF
assign SRAMZONE = |{~A23I,~A22I,A21,~A20};               // D00000 DFFFFF

assign WORDACCSS = LDS|UDS;

assign ROMOEL = ~RW | LDS | ROMZONE;
assign ROMOEU = ~RW | UDS | ROMZONE;
assign PORTOEL = ~RW | LDS | PORTZONE;
assign PORTOEU = ~RW | UDS | PORTZONE;
assign PORTWEL = RW | LDS | PORTZONE;
assign PORTWEU = RW | UDS | PORTZONE;
assign PADRS = PORTZONE;
assign WRL = ~RW | LDS | WRAMZONE;
assign WRU = ~RW | UDS | WRAMZONE;
assign WWL = RW | LDS | WRAMZONE;
assign WWU = RW | UDS | WRAMZONE;
assign SROMOEL = ~RW | LDS | SROMZONE;
assign SROMOEU = ~RW | UDS | SROMZONE;
assign SRAMOEL = ~RW | LDS | SRAMZONE;
assign SRAMOEU = ~RW | UDS | SRAMZONE;
assign SRAMWEL = RW | LDS | SRAMZONE;
assign SRAMWEU = RW | UDS | SRAMZONE;

assign DIPRD0 = ? // Asks NEO-F0 for dipswitches on D0~7 ?

// Not sure about word access, is it LDS|UDS or LDS&UDS or nothing at all ?
assign LSPOE = ~RW | WORDACCESS | LSPCZONE;
assign LSPWE = RW | WORDACCESS | LSPCZONE;
assign CRDO = ~RW | WORDACCESS | CARDZONE;
assign CRDW = RW | WORDACCESS | CARDZONE;
assign CRDC = CRDO & CRDC;

// Inter-CPU comm.
// To do

// Inputs
// To do

// Wait states
// To do