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5-6 Chapter 5: 5953 USB DynaKey Migration
The USB DynaKey implements a standard seven-port USB Hub
internally, which provides independent connectivity to the several
functional sections that comprise the DynaKey.
Both USB and Wedge NCR DynaKeys include keys that accept
customer-specified key caps and labels. For example, one customer
may wish to include buttons for DEPT, CLASS, and SKU on his
keyboard. A different customer may have no use for these keys, but
may want TIRES, BATTERIES, and ACCESSORIES on specific keys.
Capable keys provide for this customization.
Double-High / Double-Wide Keys
With capable keys you can put caps over pairs of plungers, resulting in
larger keys. On a standard keyboard, the space bar, the Enter, Tab,
Delete, Shift, Control, and Alt keys are all wider than the rest. These keys
are implemented with one or two plungers, but they cannot be
modified for different functionality. On NCR keyboards, the capable
keys may be capped in pairs. Key caps are available that cover two
plungers, either double-high or double-wide.
When two keys are capped individually, the keyboard firmware must
detect each one as a different key, and must send different messages to
the host computer to indicate that different keys were pressed. When
the same two keys are capped together, the firmware must know this
and send only one message. With the 5953 Wedge DynaKey, this is
accomplished by using firmware that senses both plungers and the
time lag between the plungers. If adjacent plungers are pressed within
a certain interval, then the firmware only sends one of the two. Which
one it sends is fixed, and the time lag is fixed. Thus, although this
method works, it is subject to occasional error due to small mechanical
tolerance problems. It is also somewhat limited in flexibility.
With the 5953 USB DynaKey, the keyboard is fully programmable. Two
keys that are capped together can be programmed to literally be
the
same key. (Duplicate messages are discarded.) Thus there is no limit to
the flexibility, and no problem can be induced by the same minor
mechanical problems experienced with the 5953 Wedge DynaKey.