C8051F709-GQR Silicon Labs, C8051F709-GQR Datasheet - Page 83

• Manufacturer Part Number: C8051F709-GQR
• Description: 8-bit Microcontrollers - MCU 8kB 32B EEPROM Cap Sense
• Manufacturer: Silicon Labs

Specifications of C8051F709-GQR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

15.4. Automatic Scanning
CS0 can be configured to automatically scan a sequence of contiguous CS0 input channels by configuring
and enabling auto-scan. Using auto-scan with the CS0 comparator interrupt enabled allows a system to
detect a change in measured capacitance without requiring any additional dedicated MCU resources.
Auto-scan is enabled by setting the CS0 start-of-conversion bits (CS0CF6:4) to 111b. After enabling auto-
scan, the starting and ending channels should be set to appropriate values in CS0SS and CS0SE, respec-
tively. Writing to CS0SS when auto-scan is enabled will cause the value written to CS0SS to be copied into
CS0MX. After being enabled, writing a 1 to CS0BUSY will start auto-scan conversions. When auto-scan
completes the number of conversions defined in the CS0 accumulator bits (CS0CF2:0), auto-scan config-
ures CS0MX to the next sequential port pin configured as an analog input and begins a conversion on that
channel. The scan sequence continues until CS0MX reaches the ending input channel value defined in
CS0SE.
Note: All other CS0 pins configured for analog input with a 0 in the port latch are grounded during the conversion.
After the final channel conversion, auto-scan configures CS0MX back to the starting input channel. For an
example system configured to use auto-scan, please see Figure “15.2 Auto-Scan Example” on page 83.
Note: Auto-scan attempts one conversion on a CS0MX channel regardless of whether that channel’s port pin has
If auto-scan is enabled when the device enters suspend mode, auto-scan will remain enabled and running.
This feature allows the device to wake from suspend through CS0 greater-than comparator event on any
configured capacitive sense input included in the auto-scan sequence of inputs.
P2MDIN = 0xF2
P3MDIN = 0x04
CS0CN = 0x80
CS0SE = 0x0D
CS0CF = 0x70
CS0SS = 0x02
been configured as an analog input. Auto-scan will also complete the current rotation when the device is halted
for debugging.
SFR Configuration:
Configures P3.0-P3.1
and P3.3-P3.7 as
analog inputs
Enables CS0
Enables Auto-scan
as start-of-
conversion source
Sets P2.2 as Auto-
scan starting channel
Sets P3.5 as Auto-
scan ending channel
Configures P2.3,
P2.2, P2.0 as analog
inputs
Figure 15.2. Auto-Scan Example
Rev. 1.0
A
D
A
A
D
D
D
D
A
A
D
A
A
A
A
A
P2.0
P2.1
P2.2
P2.3
P2.4
P2.5
P2.6
P2.7
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
10
11
12
13
14
15
0
1
2
3
4
5
6
7
8
9
C8051F70x/71x
analog inputs result
Scans on channels
values that cannot
not configured as
in indeterminate
Interrupt event
Greater Than
trigger a CS0
83