logic new201002

 

ON 20100202@1:26:27 PM at page:
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James Newton[JMN-EFP-786] Published and replied to post 40211.3686458333 by ice_chok

|Insert 'It's really pretty easy when you think about it: Use 5 2-to-4 decoders, the first one, called "E", is connected to the upper 2 bits of your 4 bit input and it then selects which of the other 4 chips will be enabled. The remaining 4 2-to-4 decoders, called "A", "B","C", and "D", each connect to the lower 2 bits of your 4 bit input and are enabled only when the 4 bit input is on their "bank" of 4 possible outputs. The first of the low bit decoders decodes 0,1,2 and 3, the second decodes 4, 5, 6, and 7, and so on.

<TABLE>
<TR>
<TD colspan=2>input</TD><TD rowspan=1>enable low<BR>bit chip #</TD>
</TR>
<TR>
<TD>decimal</TD><TD>binary</TD>
</TR>
<TR><TD>0</TD><TD><B>00</B>00</TD><TD>A</TD></TR>
<TR><TD>1</TD><TD><B>00</B>01</TD><TD>A</TD></TR>
<TR><TD>2</TD><TD><B>00</B>10</TD><TD>A</TD></TR>
<TR><TD>3</TD><TD><B>00</B>11</TD><TD>A</TD></TR>
<TR><TD>4</TD><TD><B>01</B>00</TD><TD>B</TD></TR>
<TR><TD>5</TD><TD><B>01</B>01</TD><TD>B</TD></TR>
<TR><TD>6</TD><TD><B>01</B>10</TD><TD>B</TD></TR>
<TR><TD>7</TD><TD><B>01</B>11</TD><TD>B</TD></TR>
<TR><TD>8</TD><TD><B>10</B>00</TD><TD>C</TD></TR>
<TR><TD>9</TD><TD><B>10</B>01</TD><TD>C</TD></TR>
<TR><TD>10</TD><TD><B>10</B>10</TD><TD>C</TD></TR>
<TR><TD>11</TD><TD><B>10</B>11</TD><TD>C</TD></TR>
<TR><TD>12</TD><TD><B>11</B>00</TD><TD>D</TD></TR>
<TR><TD>13</TD><TD><B>11</B>01</TD><TD>D</TD></TR>
<TR><TD>14</TD><TD><B>11</B>10</TD><TD>D</TD></TR>
<TR><TD>15</TD><TD><B>11</B>11</TD><TD>D</TD></TR>
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