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AR# 230

94 DATA BOOK 2nd: Presettable Down Counter on page 8-72 is misdrawn


The figure "Presettable Down Counter" is misdrawn. The AND gate below T5 in
the upper-right-hand corner of the drawing calculates whether bits 1-4 of the
counter are low. This is passed on to the T6 AND gate, and this gate is
supposed to make T6 active (high) when bits 5-0 of the counter are all low,
and similarly for T7 and bits 6-0 of the counter. However, the schematic as
drawn makes T6 high whenever bits 5 and 0 are low *and* at least one of bits
1-4 is high! Similarly, T7 is high whenever bits 6, 5, and 0 are low *and*
at least one of bits 1-4 is high. This also messes up the terminal count.


Fixing this can be accomplished in one of two ways:

1. Removing the second bubble down off the T6 and T7 AND gates, and the
first bubble down on the AND gate feeding the terminal-count flip-flop.

2. Placing a bubble on the output of the AND gate below T5.

The second solution was implemented in the 94 data book 3rd edition

AR# 230
日期 08/08/2000
状态 Archive
Type 综合文章