GEOS cartridge

From: Ruud_at_Baltissen.org
Date: Sun, 16 Jun 2013 22:18:53 +0200
Message-ID: <51BE1DAD.3446.14CFCDB@Ruud.Baltissen.org>
Hallo allemaal,


I just found the GEOS cartridge I mentioned a week or so ago. It 
has 'only' five parts:
- a switch between EXROM and GND to en/disable the cart
- two 27C256 EPROMs
- one unknown 14 pins IC
- one unknown 16 pins IC

Unfortunately the codes of the two ICs have been removed :( But I'm 
quite sure that the 16 pins one is a 74175. The problem: my IC 
tester says it's not. But I just had the idea to test this by 
replacing it with a marked one. (not now, tomorrow)

The 14 pins one gives me head aches:


                    +------+
          +----- 2 -+      |            +------+
PHI2 -----+         |  ??  +- 1 ---- 5 -+      |
          +----- 3 -+      |            |  ??  +- 4 --- 9 of 175
                    +------+     +-- 6 -+      |
                                 |      +------+
IO1 -----------------------------+

Pins 8..13 are not used. 


There aren't many ICs with outputs at pin 1 and 4. What immediately 
came to my mind was the 7402. But pin 9 of the 175 has a rising 
edge. OTOH, at the falling edge of IO1 the address should be valid 
as well and that could work. But again the same problem: my IC 
tester says it's not. We'll see tomorrow.

But it could be that one of you know of ICs that I don't know and 
still fit the description.


--
   
Kind regards / Met vriendelijke groet, Ruud Baltissen
www.Baltissen.org







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Received on 2013-06-16 21:00:03

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