Schematic Progress:

-Added the ~21Mhz crystal and supporting components, this connects to the CPU clock (CLK), the PPU clock (U5-CLK) and the cartridge (SYS_CLK) lines. Need to check if the NPN transistor I used in the schematic is a valid substitute for what Nintendo used.

-Added the reset switch circuit from the Famicom.

-Added the 4Mhz crystal and supporting components, this clock is used by the CIC (10NES) chips. (Both console and cartridge chips)

I need to go back and change the package size used in CIC clk circuit. 0402 is unnecessarily small, 0805 is more than small enough.

I'm numbering the passive components as I add them to my schematic, for now disregarding the numbering system obtained from the old schematics (see my research post.)

As is, the design is a hybrid of the famicom and NES. So really I've building a clone motherboard that requires 4 of the original chips: the PPU, the CPU, and the 2 ram chips. (CIC chip optional) All of the other parts I find equivalents for, with the criteria that mouser.com sells it and the part also exists in an eagle library (or eagle has a similar part of the same package size.) Eventually I'd like to create forks of the schematic, one faithful to the famicom, one faithful to the NES, and various other ones integrating mods. That being said once the hybrid schematic is complete I'll probably start playing with the board layout of my clone first, and shelve the reference schematic forks for later.

Regarding the CIC lockout chip. I had considered the standard disable method of leaving pin 4 (lock/key) disconnected (or pulled low), which changes the mode and effectively prevents the lockout chip from resetting the CPU due to poor cartridge connections. In this scenario the CIC, which is wired to the physical reset switch, will still reset the CPU when it senses that the reset button is pushed. My approach was to sever the connection from CIC pin 9 (host reset) to the CPU's reset line (/RST). This forces the use of the famicom reset circuit which connects the physical reset switch directly to /RST instead of the CIC. One benefit I see to this approach is that installing the CIC is completely optional at this point, if you don't want to bother transferring it from an old motherboard/cart to this replacement mobo that should be ok - everything will still work, including the reset button. I had considered omitting the CIC completely but I think it could be re-purposed. It was intended to be a DRM mechanism, but it also ended up being a mechanism that wouldn't allow you to play games with possibly bad cartridge connections. I'd like to turn it into a mechanism that merely indicates a connection issue, one that still allows you to play despite the warning.

Parts added in update:

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cic clock circuit

C2,C3

220pf caps

http://www.mouser.com/ProductDetail/Kemet/C0402C221J5GACTU/

http://www.mouser.com/ds/2/212/KEM_C1003_C0G_SMD-356956.pdf

0402 package size

eagle part: rcl->C-US-> C-USC0402

XTAL2

4mhz XTAL

http://www.mouser.com/ProductDetail/CTS-Electronic-Components/ATS040B/

HC49U package

crystal->8M10AHC49T

R1

1M ohm resistor

http://www.mouser.com/ProductDetail/ROHM-Semiconductor/ESR01MZPJ105/

0402 package size

rcl- > R_US -> R-US_R0402

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system clock circuit

XTAL1

21.47727mhz XTAL

http://www.mouser.com/ProductDetail/Citizen-FineDevice/HC49US-2147727MABJ-UB/

HC49US package

crystal->8M10AHC49T

R2

150 Kilo Ohm

http://www.mouser.com/ProductDetail/ROHM-Semiconductor/ESR10EZPF1503/

0805 package size

rcl- > R_US -> R-US_R0805

R3, R4

510 Ohm

http://www.mouser.com/ProductDetail/ROHM-Semiconductor/ESR10EZPJ511/

0805 package size

rcl- > R_US -> R-US_R0805

R5

220 Kilo Ohm

http://www.mouser.com/ProductDetail/ROHM-Semiconductor/ESR10EZPF2203/

0805 package size

rcl- > R_US -> R-US_R0805

C4,C5

51 pF

http://www.mouser.com/ProductDetail/Murata-Electronics/GRM0335C1E510JA01D/

0603 package size

eagle part: rcl->C-US-> C-USC0603

C6, C7

15 pF

http://www.mouser.com/ProductDetail/Murata-Electronics/GRM0335C2A150JA01D/

0603 package size

eagle part: rcl->C-US-> C-USC0603

C8

30 pF

http://www.mouser.com/ProductDetail/Murata-Electronics/GRM0335C1H300GA01D/

0603 package size

eagle part: rcl->C-US-> C-USC0603

Q1,Q2

2SC2021 Transistor is noted as original

Epitaxial Planar NPN Silicon Transistor / General Small Signal Amp

http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/Bipolar-Transistors-BJT/_/N-ax1sh/

Replacement http://www.mouser.com/ProductDetail/ON-Semiconductor/2SD1048-7-TB-E/

http://www.mouser.com/ds/2/308/EN694-D-310421.pdf

package: SOT23 aka TO-236

eagle part substitute: transistors-npn -> BC848* -> BC848SMD

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Reset circuit

C1 0.47u

http://www.mouser.com/ProductDetail/Kemet/RSBDC3470AA10J/

http://www.mouser.com/ds/2/212/KEM_F3067_RSB-540779.pdf

eagle part: rcl->C-US->C-US050-035X075 [C050-035X075]

Reset Switch

http://www.mouser.com/ProductDetail/CHERRY/MX1A-E1NW/

http://www.mouser.com/ds/2/71/mx_cat-216303.pdf

eagle library: https://github.com/c0z3n/cherrymx-eagle ; cherrymx.lbr

eagle part: cherrymx ->CHERRY-MX

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