WM8581 Wolfson Microelectronics Ltd., WM8581 Datasheet - Page 75

• Manufacturer Part Number: WM8581
• Description: Multichannel Codec with S/pdif Transceiver
• Manufacturer: Wolfson Microelectronics Ltd.

Production Data
HARDWARE CONTROL MODE
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Figure 35 and Figure 36 show typical power up scenarios in a real system. Both AVDD and DVDD
must be established, and VMID must have reached the threshold Vporr before the device is ready
and can be written to. Any writes to the device before Device Ready will be ignored.
Figure 35 shows DVDD powering up before AVDD. Figure 36 shows AVDD powering up before
DVDD. In both cases, the time from applying power to Device Ready is dominated by the charge time
of VMID.
A 4.7µF capacitor (minimum) is recommended for decoupling on VMID. The charge time for VMID
will dominate the time required for the device to become ready after power is applied. The time
required for VMID to reach the threshold is a function of the VMID resistor string and the decoupling
capacitor. To reduce transient audio effects during power on, the stereo DACs on the WM8581 have
their outputs clamped to VMID at power-on. This increases the capacitive loading of the VMID
resistor string, as the DAC output AC coupling capacitors must be charged to VMID, and hence the
required charge time. To ensure minimum device startup time, the VMIDSEL bit is set by default,
thus reducing the impedance of the resistor string. If required, the VMID string can be restored to a
high impedance state to save power once the device is ready.
DEVICE ID READBACK
Reading from registers R0, R1 and R2 returns the device ID and revision number. R0 returns 80h, R1
returns 85h, R2 returns the device revision number. Device ID readback is not possible in continuous
readback mode (CONTREAD=1).
The WM8581 can be controlled in Hardware Control Mode or Software Control Mode. The method of
control is determined by the state of the HWMODE pin. If the HWMODE pin is low, Software Control
Mode is selected. If the HWMODE pin is high, Hardware Control Mode is selected.
In Hardware Control Mode the user has limited control over the features of the WM8581. Most of the
features will assume their default settings but some can be modified using external pins.
DIGITAL ROUTING CONTROL
See page 25 for a more detailed explanation of the Digital Routing Options within the WM8581. In
Software Control Mode, the values of register bits DAC_SRC, PAIFTX_SRC and TXSRC configure
the signal path routing between interfaces. In hardware mode, similar control can be achieved via
pins DR1, DR2, DR3 and DR4 as detailed in Table 69 and Table 70.
Table 68 Hardware/Software Mode Setup
Table 69 DR1 / DR2 Operation
Software Control Hardware Control
REGISTER ADDRESS
ADC CONTROL 1
0
R29
1Dh
DR1
DR2
PIN
HWMODE
BIT
1
8
DAC_SRC=S/PDIF receiver
PAIFTX_SRC=S/PDIF
VMIDSEL
LABEL
2-wire control
receiver
0
0
DEFAULT
SWMODE
1
3-wire control
0 = High impedance, power
saving
1 = Low impedance, fast power-
on
VMID Impedance Selection
PAIFTX_SRC=ADC output
DAC_SRC=PAIF receiver
1
DESCRIPTION
1
PD Rev 4.0 April 2007
WM8581
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