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4-4 Chapter 4: Programming
The MSR interface: The MSR conforms to the USB HID standard
for MSRs as described in the HID Usage Tables for POS, Ver 1.02,
see http://www.usb.org/developers/hidpage.html#pos
.
The Key Matrix: The Key Matrix report contains an overlay for the
keyboard look-up table. It is organized in FPGA Offset order, and
contains pairs of 8-bit usages, one pair per key position. Values of
zero produce no usage report. Two different usages produce two
simultaneous usages being reported. The number of positions is
given by the report descriptor.
Programmable Key Matrix
The keyboard matrix is completely programmable, translating between
a key switch physical location and the key data reported to the host PC.
Through this keyboard provision, you can switch the numeric keypad
layout from the default calculator layout to a telephone layout by
organizing the keyboard matrix to mimic either mode of operation.
Note: If you change the numeric keypad layout, you must also
physically remove and swap the key caps on the first and third rows of
the keypad. The key codes for the numeric keypad are identical to the
IBM PS/2, 101-key keyboard.
Double-high/Double-wide Keys
Several keys on the keyboard can accept optional keycaps that cover
two keys to produce double-high or double-wide keys. When you
press a double-high or double-wide keycap, the keyboard firmware
sends the keycode for both keys. When usages are the same, only one
keycode is sent. Using the programmable key matrix feature, the
keyboard matrix can be programmed to support double-high or
double-wide keys by specifying the same key code for both key
locations supported by the key cap.