Matrix Orbital VK204-25 Legacy - Manual (Page 20)

In this mode, when a key is held down, the key code is transmitted immediately and no other codes will be
sent until the key is released. On the release of the key, the key release code transmitted will be a value equal
to the key down code plus 20 hex. For example, the key code associated with key ’P’ (0x50) is pressed, the
release code is ’p’ (0x70). In RS-232 polled mode or via the I 2 C interface, the “Key down / key up codes”
are used. However, the user should be careful of timing details. If the poll rate is slower than the simulated
auto-repeat it is possible that polling for a key up code will be delayed long enough for an unwanted key
repeat to be generated.
Figure 15: Poll Timing
4.5.2 Auto repeat mode off (254 96)
This command turns off auto repeat mode.
4.5.3 Auto transmit keypresses on (254 65)
In this mode, all keypresses are sent immediately to the host system without the use of the poll keypad
command. This is the default mode on power up.
4.5.4 Auto transmit keypresses off (254 79)
In this mode, up to 10 keypresses are buffered until the unit is polled by the host system via the poll
keypad command. Issuing this command places the unit in polled mode.
4.5.5 Clear key buffer (254 69)
This command clears any unread keypresses. In a menuing application, if the user presses a key which
changes the menu context, any following key presses may be inaccurate and can be cleared out of the buffer
between menu changes to prevent jumping around the menu tree. It may also be used to, in effect, reset the
keypad in case the host application resets for whatever reason.
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