Appeal No. 97-1694
Application 08/351,064
connects the bus wire to ground when switched on (col. 4,
lines 29-35) and an associated precharge circuit 16 which
dumps a prescribed amount of charge onto the bus at the moment
of each expected transition of the bus to precharge the
capacitance represented by the bus wire itself and the bus
driver transistor (col. 4, lines 36-44). The precharge
transistor and the bus driver transistor may be combined in
the arrangement shown in figure 4 (col. 5, lines 9-34).
Although the circuit arrangement in figure 4 looks like
appellants' push-pull output circuit 236,
it does not function as one because the transistors do not
operate
in phase opposition to both source current to and sink current
from the bus. The precharge transistor 42 only adds a small
amount of charge and the driver transistor delivers about 40
times the amount of current (col. 5, lines 18-21). The
wire-OR bus is brought to its high state when the active
pull-down device releases the bus, not by the use of a pull-up
device. Lloyd discloses that a tri-state bus using pull-up
and pull-down devices was known in the prior art (col. 1,
- 6 -
Page: Previous 1 2 3 4 5 6 7 8 9 10 11 12 13 Next
Last modified: November 3, 2007