CYW20734
1.8.3 Scan
In the scan state, a row counter counts from 0 up to a programmable number of rows minus 1. After the last row is reached, the row
counter is reset and the column counter is incremented. This cycle repeats until the row and column counters are both at their
respective terminal count values. At that point, the state machine moves into the Scan-End state.
As the keys are being scanned, the key-index counter is incremented. This counter value is compared to the modifier key codes stored
in RAM, or in the key-code buffer if the key is not a modifier key. It can be used by the microprocessor as an index into a lookup table
of usage codes.
Also, as the nth row is scanned, the row-hit register is ORed with the current 8-bit row input values if the current column contains two
or more row hits. During the scan of any column, if a key is detected at the current row, and the row-hit register indicates that a hit
was detected in that same row on a previous column, then a ghost condition may have occurred, and a bit in the status register is set
to indicate this.
1.8.4 Scan End
This state determines whether any keys were detected while in the scan state. If yes, the state machine returns to the scan state. If
no, the state machine returns to the idle state, and the 128 kHz clock request signal is made inactive.
Note: The microcontroller can poll the key status register.
1.9 Mouse Quadrature Signal Decoder
The mouse signal decoder is designed to autonomously sample two quadrature signals commonly generated by an optomechanical
mouse. The decoder has the following features:
■ Three pairs of inputs for X, Y, and Z (typical scroll wheel) axis signals. Each axis has two options:
❐ For the X axis, choose P2 or P32 as X0 and P3 or P33 as X1.
❐ For the Y axis, choose P4 or P34 as Y0 and P5 or P35 as Y1.
❐ For the Z axis, choose P6 or P36 as Z0 and P7 or P37 as Z1.
■ Control of up to four external high-current GPIOs to power external optoelectronics:
❐ Turn-on and turn-off time can be staggered for each HC-GPIO to avoid simultaneous switching of high currents and having multiple
high-current devices on at the same time.
❐ Sample time can be staggered for each axis.
❐ Sense of the control signal can be active high or active low.
❐ Control signal can be tristated for off condition or driven high or low, as appropriate.
1.9.1 Theory of Operation
The mouse decoder block has four 10-bit PWMs for controlling external quadrature devices and sampling the quadrature inputs at its
core.
The GPIO signals may be used to control such items as LEDs, external ICs that may emulate quadrature signals, photodiodes, and
photodetectors.
1.10 ADC Port
The ADC block is a single switched-cap Σ-∆ ADC core for audio and DC measurement. It operates at the 12 MHz clock rate and has
32 DC input channels, including 28 GPIO inputs. The internal bandgap reference has ±5% accuracy without calibration. Different
calibration and digital correction schemes can be applied to reduce ADC absolute error and improve measurement accuracy in DC
mode.
1.11 Microphone Input
The CYW20734 integrates support for a differential or single-ended mono microphone. This reduces the requirement on external
components because there is no need for a separate microphone amplifier. The microphone input has a user-programmable gain
range of 0–42 dB with 3 dB steps. A microphone bias output from the chip is provided that can be used to bias an electret condenser-
type microphone. The MIC Bias reference output voltage is 2.1V or 21/25 of the audio power supply. The MIC block can be powered
down when it is not in use.
Document Number: 002-14874 Rev. *S
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