Re: More on the 8701 clock chip (fwd)

From: Marko Mäkelä (
Date: 1998-02-13 09:28:33

Does anyone any interest in hacking with the 8701 chip?  BTW, if you touch
the pins 14-16 with your finger, the main frequency will collapse. :-)

---------- Forwarded message ----------
Date: Thu, 12 Feb 1998 22:35:05
From: "William M. Levak" <>
To: Marko Mäkelä <Marko.Makela@HUT.FI>
Subject: Re: More on the 8701 clock chip

The pinout of the clock chip as obtained from The schematics is as

                              1    16
                         GND  2    15  +5V                
                              3    14  crystal in
                         GND  4    13  crystal out
                              5    12  +5V
                   dot clock  6    11  
                  enable PAL  7    10
                 color clock  8     9  GND

I have been experimenting on the chip and have discovered the following:

1.  If you disconnect pin 12, the entire chip is dead.  If you disconnect
pin 15, the crystal stops oscillationg and all outputs stay at a constant
level, but the chip is not dead.  Therefore, pin 12 is the true Vcc and
pin 15 is the 5V level for the crystal.

2.  If you disconnect pin 9, all functions on the chip stop.  If you
disconnect pin 2, the outputs stop, but the crystal still oscillates.  If
you disconnect pin 4, an output appears on pin 11.  Therefore, pin 9 is
the true Vss, pin 2 is the output enable, and pin 4 is the enable for pin

3.  If you ground pin 5, the dot clock stops.

4.  Pin 10 maintains a constant output at 5V.

5.  I have found no functions fro pins 1, 3 and 16.

If you incorporate all this information into a pinout, it woul lokk like
the following:

                              1    16
               output enable  2    15  +5V for crystal
                              3    14  crystal in
              disable pin 11  4    13  crystal out
           disable dot clock  5    12  Vcc
                   dot clock  6    11  unknown output
                  enable PAL  7    10  5V constant output
                 color clock  8     9  Vss

        Enable or disable is accomplished by tying to ground. 

This is, of course, very tentative, until I or someone else can think of
more tests.

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