WM9715L Datasheet, PDF (43/77 Pages) Wolfson Microelectronics plc – AC’97 Audio and Touchpanel CODEC

Production Data
INITIATION OF MEASUREMENTS
WM9715L
The WM9715L touchpanel interface supports both polling routines and DMA (direct memory access)
to control the flow of data from the touchpanel ADC to the host CPU.
In a polling routine, the CPU starts each measurement individually by writing to the POLL bit (register
76h, bit 15). This bit automatically resets itself when the measurement is completed.
REGISTER
BIT
LABEL DEFAULT
ADDRESS
DESCRIPTION
76h
10
CTC
0
0: Polling mode
1: Continuous mode (for DMA)
15
POLL
0
Writing “1” initiates a measurement
9:8
CR
00
Continuous mode rate (DEL ≠ 1111)
00: 93.75 Hz (every 512 AC-Link frames)
01: 187.5 Hz (every 256 AC-Link frames)
10: 375Hz (every 128 AC-Link frames)
11: 750Hz (every 64 AC-Link frames)
Continuous mode rate (DEL = 1111)
00: 8 kHz (every six AC-Link frames)
01: 12 kHz (every four AC-Link frames)
10: 24 kHz (every other AC-Link frame)
11: 48 kHz (every AC-Link frame)
78h
11
PDEN 0
0: measure regardless of pen status
1: measure only when pen is down (when
CTC=0 and POLL=1, measurement is
delayed until pen-down; when CTC=1,
measurements are stopped on pen-up)
Table 25 Touchpanel Digitiser Control (Initiation of Measurements)
In continuous mode (CTC = 1), the WM9715L autonomously initiates measurements at the rate set
by CR, and supplies the measured data to the CPU on one of the unused AC’97 time slots. DMA-
enabled CPUs can write the data directly into a FIFO without any intervention by the CPU core. This
reduces CPU loading and speeds up the execution of user programs in handheld systems.
Note that the measurement frequency in continuous mode is also affected by the DEL bits (see
“Touchpanel Settling Time”). The faster rates achieved when DEL = 1111 may be useful when the
ADC is used for auxiliary measurements.
MEASUREMENT TYPES
The ADCSEL control bits determine which type of measurement is performed (see below).
REGISTER BIT
ADDRESS
LABEL DEFAULT
DESCRIPTION
76h
14:12 ADCSEL 000
Measurement Type (ADC Input Selector)
000: No measurement
001: X co-ordinate measurement
010: Y co-ordinate measurement
011: Pressure measurement
100: COMP1/AUX1 measurement (pin 29)
101: COMP2/AUX2 measurement (pin 30)
110: BMON/AUX3 measurement (pin 31)
111: WIPER/AUX4 measurement (pin 12)
11
COO
0
Enable co-ordinate mode
0: Single measurement according to ADCSEL
1: X, then Y, then additional measurement
indicated by ADCSEL
Table 26 Touchpanel Digitiser Control (Measurement Types)
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PD Rev 4.0 December 2007
43