Appeal No. 2002-1735 Page 2
Application No. 08/903,878
Conventionally, parallel communication via a Centronics interface or a Small
Computer System Interface and serial communication via a RS-232C, a RS-422, or an
Universal Serial Bus are used to transmit image data from a printer controller to a
printer. According to these protocols, explain the appellants, image data are
transmitted from the printer controller to the printer irrespective of the printing speed of
the printer. (Id.) Consequently, they add, the printer must be provided with enough
storage capacity to store image data representing at least one frame of an image (the
image printed on one sheet of paper). (Id. at 1-2.)
In contrast, the appellants' printer controller sends a start signal to an associated
printer. (Id. at 67.) Upon elapse of a fixed time following transmission of the signal, the
printer controller "isochronous[ly],"1 (id.), transfers image data to be printed to the
printer. Because the image data are transferred "from the printer controller to the
printer at [a] fixed period, printing can be done at a constant speed without requiring
that the printer be provided with an image memory for storing image data representing
one frame of an image." (Id.) The requirement for smaller storage capacity, "lower[s]
the cost of the printer." (Id. at 6.)
1"With isochronous transfer, data referred to as cycle-start packet data [are] in
principle generated at an isochronous cycle (125 :s) by any of a plurality of nodes
connected by a bus. Data [are] transmitted from a certain node (this node is a cycle
master, as will be described later) to another node every isochronous cycle." (Spec.
at 2.)
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