CYW20738
1.2 Mouse Quadrature Signal Decoder
The mouse signal decoder is designed to autonomously sample two quadrature signals commonly generated by optomechanical
mouse apparatus. 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.
1.2.1 Theory of Operation
The mouse decoder block has four 16-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.
1.3 Infrared Modulator
The CYW20738 includes hardware support for infrared TX. The hardware can transmit both modulated and unmodulated waveforms.
For modulated waveforms, hardware inserts the desired carrier frequency into all IR transmissions. IR TX can be sourced from
firmware-supplied descriptors, a programmable bit, or the peripheral UART transmitter.
If descriptors are used, they include IR on/off state and the duration between 1–32767 µsec. The CYW20738 IR TX firmware driver
inserts this information in a hardware FIFO and makes sure that all descriptors are played out without a glitch due to underrun. See
Figure 2.
Figure 2. Infrared TX
VCC
R1
62
INFRARED-LD
U1
D1
R2
20738
Q1
MMBTA42
IR TX
2.4K
Document Number: 002-14891 Rev. *C
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