It is currently Mon Sep 16, 2019 1:58 am

All times are UTC - 7 hours





Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: Sun Sep 08, 2019 1:26 pm 
Offline

Joined: Sun Jun 12, 2011 12:06 pm
Posts: 540
Location: Poland
One guy asked me to analyze this cartridge. Fortunatelly there were photos of PCB on the web so I give a chance.
There is one think I cannot agree with the Mapper 105 description:
Quote:
On powerup and reset, the first 32k of PRG (from the first PRG chip) is selected at $8000 *no matter what*.
PRG cannot be swapped until the mapper has been "initialized" by setting the 'I' bit to 0, then to '1'. This
toggling will "unlock" PRG swapping on the mapper.

Because the MMC1-PRG-A14 is directly connected to both EPROMS, if MMC1 is switched into 16K+16K mode and MMC1 PRG's bank is modified, $8000 might stop pointing to first 32k even without rising edge on `I` bit.

Image Image Image Image Image


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 3:00 am 
Offline

Joined: Mon Apr 24, 2017 10:23 pm
Posts: 8
Probably pull-up resistors are missing for 74hc30


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 4:04 am 
Offline

Joined: Sun Jun 12, 2011 12:06 pm
Posts: 540
Location: Poland
Yes sorry, I did not notice there is VCC pull-up 4xresistor ladder above the switch (if that were LS, not HC - pull-ups wouldnt be needed)


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 6:12 am 
Offline

Joined: Fri Feb 24, 2012 12:09 pm
Posts: 1003
Those 4-in-1 resistor components are called "resistor networks".
A resistor ladder is something else (a circuit related to digital/analog conversion).
Either way, it's hard to see on the photo, I wasn't sure what you were talking about, until noticing the "shadow" behind the DIP switches.

_________________
homepage - patreon


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 1:46 pm 
Offline

Joined: Mon Jan 23, 2012 11:27 pm
Posts: 169
Kevtris' writeup mentions the cic reset line is connected to something else on the board, what's going on with that?


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 1:58 pm 
Offline

Joined: Sun Apr 13, 2008 11:12 am
Posts: 8557
Location: Seattle
CIC reset is used to force the game into the menu on reset, instead of using a diode, resistor, and capacitor to detect A0 or M2 going high impedance.


Top
 Profile  
 
PostPosted: Mon Sep 09, 2019 2:31 pm 
Offline

Joined: Sun Jun 12, 2011 12:06 pm
Posts: 540
Location: Poland
I fixed the schematic - pin 7 of CIC is the one used to detect reset and which comes from edge connector, not pin 9.
Image

I like how Nintendo routed all pins of all chips either out of the board or to to a place where a hole was drilled,, even those non connected to anything to short them while gold plating. That helps in guessing!


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: Google [Bot] and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group