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Santucci4



Joined: 08 May 2008
Posts: 44
Location: Illinois

PostPosted: Thu Jun 12, 2008 4:10 pm    Post subject: Router Configuration Register Reply with quote

I am a little lost on this Configuration Register and can't figure it out when I thought I did understand it. Here's my problem.

The configuration register contains 4 nibbles with 16 bits. Now each of those bits controls a function which I get. Each nibble has a value of 1,2,4, or 8. Now, with bits 2,5,9 and 14 turned on, you get a value of the 0x2102. In my book that I'm reading by Todd Lammle, he says that once you turn on bit 6, you now get a value of 0x2142. When I look at the chart in the book and count the bit markers, bit 6 is supposed to be a 5 value making it 0x2152. I know that I'm wrong; but I can't see how the book is coming up with that value unless I'm reading the chart wrong.

Thanks,
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wingchunbr



Joined: 28 Jun 2008
Posts: 6

PostPosted: Sat Jun 28, 2008 1:18 am    Post subject: Reply with quote

0x2102 = 0010 0001 0000 0010 (2,9,14 bits on)
0x2142 = 0010 0001 0100 0010 (2,7,9,14 bits on)
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crissa



Joined: 23 Nov 2007
Posts: 792
Location: Dortmund, Germany

PostPosted: Sat Jun 28, 2008 7:17 am    Post subject: Reply with quote

wingchunbr wrote:
0x2102 = 0010 0001 0000 0010 (2,9,14 bits on)
0x2142 = 0010 0001 0100 0010 (2,7,9,14 bits on)


Hello,
according the table 5.2 on page 254 (Todd Lammle, CCNA study guide, 6th edition) you count the bits (of a binary value) from 0 to 15!

And even if you say it is the third bit of the second nibble (countiong from the right and starting with 1) it is still the 6 bit of the binary value (starting from the right and starting with 0).


0x2102 = 0010 0001 0000 0010 => bits 1, 8 and 13 on
0x2142 = 0010 0001 0100 0010 => bits 1, 6, 8 and 13 on

bit 6 => ignore NVRAM contents


BTW, I know the book has some errors and typos, but we can check the Cisco website: Use of the Configuration Register on All Cisco Routers
And they also start to count the bits from the right starting with 0.

HTH!
Bye, Tore

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wingchunbr



Joined: 28 Jun 2008
Posts: 6

PostPosted: Tue Jul 08, 2008 2:21 am    Post subject: Reply with quote

you are right crissa
i forgot start counting from 0
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