Serial Wombat
a general-purpose digital interface
device for hobbyists, engineers and students
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Serial Wombat Transition Counter Mode
The Serial Wombat can count transitions on a pin. It can increment a counter on low-to-high, high-to-low, or both transitions. Software debouncing is optional to quiet down noisy sources like mechanical switches. The user can configure a maximum value, and if the counter rolls over to zero, or stays at maximum. The count is put in the pin's public data buffer.
This mode is useful for a variety of things, such as counting the number of button presses by a user. By allowing the Wombat to keep count, the host doesn't have to constantly poll the state of the pin.
Note that transitions which occur faster than the frame frequency may be missed.
Faster pulse counts for measurement of very fast events can be acheived with the hardware pulse measurement mode on capable pins.
Message format:
| Data Sent to the Wombat: | 200 | Pin # | 13 | Debounce frames MSB | Debounce frames LSB | Transition type: | Maximum MSB | Maximum LSB |
| Meaning: | Configure Pin First message | Pin Number to be set to Counter | Counter | A transition must differ from the current state for this many frames in order to be detected | 0: Count Low to High
Transitions 1: Count High to low Transitions 2: Count both transitions. Add 16 (0x10) to the value if the counter should NOT roll over after maximum. |
The maximum value the counter can attain. Depending on the value of byte 5, the counter will either stop at this value, or roll over to zero. | ||
| This message is echoed back by the Wombat. | ||||||||
Example:
Pin 37 is tied to ground through a push-button switch. Internal pull-up resistors are enabled. When the button is pressed, it will transition from high to low. Configure channel 37 to count button presses. Require the switch to maintain a value for 30 frames (assume 1ms per frame) to debounce this value. Allow a maximum value of 65535, and stop rollover.
200 37 13 0x001E 0x111 0xFFFF ; Set pin 37 to counter mode,
; 30 frame debounce (0x01E)
; High to Low transitions, no rollover (0x11)
; Maximum of 65535