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 Post subject: SKROM Schematic?
PostPosted: Mon Feb 03, 2014 4:04 am 
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Is there any schematic for SKROM?


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 Post subject: Re: SKROM Schematic?
PostPosted: Mon Feb 03, 2014 1:28 pm 
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SKROM should be the "platonic" fully-populated MMC1 board, with everything specified on the wiki's pinout connected to the corresponding pins on the ROMs and RAMs.


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 Post subject: Re: SKROM Schematic?
PostPosted: Mon Feb 03, 2014 3:09 pm 
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Thanks for the reply
I found these pinout related to SKROM, most of them should be correct but obviously it is incomplete because of missing other parts including capacitors, resistors, and diodes :

Image


Can you help me to find out their value :

Image


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 Post subject: Re: SKROM Schematic?
PostPosted: Mon Feb 03, 2014 3:22 pm 
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The top resistor is 1k, and the one below the diode is 10k. The one on the right is 27k.

As for the capacitors, their values doesn't really matter as they are bypass caps. Usually those are between 10n and 100n. The big electrolytic caps should be more, their values is often printed straight on them.

By the way SKROM is definitely the most "typical" MMC1 circuit you can find : All the lines are used, including high address lines and WRAM, and there is no "funky" wiring either such as what is done in SUROM (CHR lines used as PRG bankswitching), or even SNROM (one of the CHR lines is used as SRAM enable).


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 Post subject: Re: SKROM Schematic?
PostPosted: Mon Feb 03, 2014 3:48 pm 
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Thanks for the help
And here is about : MOBILE SRAM MEMORY
Are diodes 1N4148?
What about the resistor shaped cap near the PRG on the edge of the board?

Edit :
Found this also
It is called axial capacitor :
Image

Can anyone tell me the color of it?


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 5:54 am 
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OK, I found a SKROM :

Front :
Image

Back :
Image

Front Scan :
Image

Back Scan :
Image

Schematic :
Image

Anyone would like to analyze the analog part of the circuit?
Especially about the function of R1, R3, D2
C2 colors are Thick Brown, Black(0), Orange(3), Green(-), Brown. So it is 3pF? Is there such a capacitor?


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 6:16 am 
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Quote:
So it is 3pF? Is there such a capacitor?

Nope, that'd be comparable to the capacity of a wire !
You read it backwards, it's 18nF.

I think you forgot on your shematic that pins 1 and 28 of WRAM are connected together (WRAM-VCC).
D2 and D1 serves to switch the correct supply to WRAM : VCC when the game is turned on, and the battery when the game is turned off. R2 is here to artificially increase the internal resistance of the battery, very likely, to prevent the battery from powering the circuit at all when turned on (the WRAM chip draws a lot more current than when idle).
CB or whathever name it is, is here to prevent sharp voltage transitions on WRAM-VCC. When the power is turned off, the voltage will slowly decrease from 5V to 3V instead of doing a sharp edge. Earlier MMC1 boards lacked this cap, the saves were lost more frequently (unless it was something else ?).

R1 is here to disable the WRAM when the power is off. I'm not sure what R3 does. It seems to attemps to force the address like A14 down (out of the $6000-$7FFF region) when power would be half-on, on enough to have the CPU doing ghost writes, but not on enough to drive the address lines properly. I wonder if this had any effect at all.


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 7:56 am 
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@ Bregalad
Thanks for the great info
But still I think C2 isn't 18nF

According to the above table :
A , B , C , D , E
Temp , 1D , 2D , M , Tol
Thick Brown, Black, Orange, Gray, Brown
-30 , 0 , 3 , 0.01 , +-1

So it should be 0.03pF!!!
But then again in my former post 3pF is not bad because if you look at the table it says something for Tolerance :
More than 10pF / Less than 10pF


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 11:55 am 
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FARID wrote:
According to the above table :
Temp , 1D , 2D , M , Tol
The very few color-band-labelled capacitors I've seen have used a much more traditional resistor-like ordering:
1D, 2D, M, Tol, Temp or Voltage
e.g. http://www.csgnetwork.com/capcccalc.html

By that analysis, it's brown, black, orange : 104 = 100nF
which is much more plausible for a bypass capacitor, too.


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 12:20 pm 
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Pehaps it's just me but I was reading :
Brown - gray - orange
which means (ignoring tolerance and other shit) : 1, 8, * 10^3, so that'd be 18 kpF = 18nF.

If it reads in the other direction then I'm messing up and sorry about it.


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 Post subject: Re: SKROM Schematic?
PostPosted: Tue Feb 04, 2014 12:45 pm 
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The cathode of D2 should connect to pin28 with everything else, not pin1 which is not connected to the die.

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