wm9714l Wolfson Microelectronics plc, wm9714l Datasheet - Page 65

• Manufacturer Part Number: wm9714l
• Description: Ac?97 Audio Codec
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
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INITIATION OF MEASUREMENTS
The WM9714L AUXADC interface supports both polling routines and DMA (direct memory access) to
control the flow of data from the AUX ADC to the host CPU.
In a polling routine, the CPU starts each measurement individually by writing to the POLL bit (register
74h, bit 9). This bit automatically resets itself when the measurement is completed.
Table 47 AUX ADC Control (Initiation of Measurements)
In continuous mode (CTC = 1), the WM9714L autonomously initiates measurements (or sets of
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. The
faster rates achieved when DEL = 1111 may be useful when the ADC is used for multiple
measurements.
74h
76h
REGISTER
ADDRESS
9
8
9:8
BIT
POLL
CTC
CR
LABEL
0
0
00
DEFAULT
Poll Measurement Control
Writing “1” initiates a measurement (when
CTC=0)
AUXADC Measurement Mode
0 = Polling mode
1 = Continuous mode (for DMA)
Continuous Mode Conversion Rate
Continuous mode rate (DEL ≠ 1111)
00: 93.75 Hz (every 512 AC-Link frames)
01: 120 Hz (every 400 AC-Link frames)
10: 153.75 Hz (every 312 AC-Link frames)
11: 187.5Hz (every 256 AC-Link frames)
Continuous mode “fast 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)
DESCRIPTION
PP, Rev 3.2, October 2008
WM9714L
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