PKP
VS1000 P
ROGRAMMER
’
S
G
UIDE
VSMPG
12.2.2
USB powering
When USB is active, USB requires at least 3.5V, which is more than the default IOVDD
value, so the voltage for the USB pins is taken from AVDD output of the internal voltage
regulator.
12.2.3
SCI_STATUS: System Flags
The SCI_STATUS register is the second System Controller register. It is used to control
and read the state of several system level peripherals.
SCI_STATUS Bits (r/w)
Name
Bits
Description
SCISTF_SLOW_CLKMODE
15
Divide XTALI by 256
SCISTF_USB_DN_OUT
14
D- pin output state in GPIO mode
SCISTF_USB_DP_OUT
13
D+ pin output state in GPIO mode
SCISTF_USB_DDR
12
Drive D+/D- pins directly as GPIO
SCISTF_VCM_OVERLOAD
11
VCM pin overload, CBUF disconnected
SCISTF_VCM_DISABLE
10
Disable VCM protection
SCISTF_USB_DP
9
State of D+ pin
SCISTF_USB_DN
8
State of D- pin
SCISTF_USB_DIFF_ENA
7
Enable USB data input
SCISTF_USB_PULLUP_ENA
6
Activate 1.5kOhm D+ pull-up resistor
SCISTF_REGU_POWERLOW
5
Regulator input too low for good AVDD
SCISTF_REGU_POWERBUT
4
State of Power Button (“Play/Pause”) pin
SCISTF_ANADRV_PDOWN
3
Analog Output Driver power down control
SCISTF_ANA_PDOWN
2
Analog Core (bias) power down control
SCISTF_REGU_CLOCK
1
Clock in new regulator voltage values
SCISTF_REGU_SHUTDOWN
0
Regulator Shutdown control
12.2.4
USB detection
USB detection and device attachment/detachment are handled using the System Con-
troller. Actual USB data traffic is handled using the USB peripheral itself.
It is suggested that bot the D+ and D- pins have a 1 megaohm pull-up resistor on the
PCB. This makes both D+ and D- pins weakly bias to “1” state when the device is not
connected to a USB port. When the USB cable is attached, the 15 kilo-ohm pull-down
resistors of the host USB hub pull D+ and D- low, pulling the pins to “0” state. Thus
detecting SCISTF_USB_DN = 0 indicates USB cable connect.
Upon detecting the connection of the USB cable, software should switch to USB volt-
ages, change the system clock to 48 MHz (XTALI=12.000MHz, Clock Multiplier 4.0x) and
wait for the clock to stabilize before setting SCISTF_USB_PULLUP_ENA high, which
activates the integrated 1.5 kilo-ohm pull-up resistor of D+, signaling the PC to start
enumeration of the USB device.
Rev. 0.20
2011-10-04
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