VK202-25 rev. 05
19
unwanted auto-repeat
after key-up.
Polls
Key down
Key up
auto-repeat clock
valid key stroke
(before key up)
Figure 4-2 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.
4.5.6 Poll keypad (254 38)
This command returns any unbuffered keypresses via the RS - 232 interface. The host system must be set up
to receive the key codes. When the VK202-25 receives this command it will immediately return any
unbuffered keypresses which may have not been read already. If there is more than one keypress buffered,
then the high order bit (MSB) of this returned keycode will be set (1). If this is the only buffered keypress,
then the MSB will be reset (0). If there are no buffered keypresses, then the returned code will be 0x00.
Please note to make use of this command the “Auto Transmit Keypress” mode should be off.
4.5.7 Set debounce time (254 85 [time])
[time] is in increments of 6.554 milliseconds.
This command sets the time between key press and key read. All key types with the exception of latched
piezo switches will “bounce” for a varying time, depending on their physical characteristics. The default
debounce time for the module is about 52 mS, which is adequate for most membrane keypads. This time
equates to a setting of 8 using this command as there is a debounce time resolution of 6.554 milliseconds.
electronic components distributor
