Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 23
 Negative Noise Threshold: Set equal to Noise Threshold
 Low Baseline Reset: Set to 10
3.7 CSD User Module Low-Level Parameters
The CSD User Module has several low-level parameters in addition to the high-level parameters. These parameters
are specific to the CSD sensing method and determine how raw count data is acquired from the sensor.
3.7.1 Scanning Speed
This parameter sets the sensor scanning speed. Although a faster scanning speed provides a good response time,
slower scanning speeds give the following advantages:
 Improved SNR
 Better immunity to power supply and temperature changes
 Less demand for system interrupt latency; you can handle longer interrupts
 See Table 3-1 and Table 3-2 for scanning speed and resolution performance.
 Possible values are Ultra Fast, Fast, Normal, and Slow.
3.7.2 Resolution
This parameter determines the scanning resolution in bits. The maximum raw count for scanning resolution of N bits
is 2
N-1
. Increasing the resolution improves sensitivity and SNR, but reduces scan time. See Table 3-1 and Table 3-2
for scanning speed and resolution performance. Possible values are 9 to 16 bits.
Table 3-1. Scanning Speed and Resolution for 24-MHz IMO Operation, without Clock Prescaler (PRS16
Configuration)
Resolution
(bits)
Scanning Speed (µs)
Ultra Fast
Fast
Normal
Slow
9 75 110 170 300
10 110 170 300 510
11 170 300 510 1010
12 300 510 1010 2030
13 510 1010 2030 4060
14 850 1690 3380 6760
15 1520 3040 6080 12200
16 2880 5720 11500 23200
Table 3-2. Scanning Speed and Resolution for 24- MHz IMO Operation, with Prescaler (PRS8 Configuration)
Resolution
(bits)
Scanning Speed (µs)
Ultra Fast
Fast
Normal
Slow
9 60 85 150 255
10 85 150 255 510
11 150 255 510 1020
12 255 510 1020 2040
13 510 1020 2010 4080
14 845 1700 3380 6760
15 1530 3060 6120 12100
16 2880 5800 11500 23000