User`s manual

Am186
TM
CC Microcontroller ISDN TA Reference Design Manual
2-11
USB PC Interface
The ISDN TA reference design has an integrated USB peripheral controller with
a built in transceiver; differential USB signals connect directly to the controller
without requiring an external transceiver. A USB type B connector is used for
connection to a PC. The N MOSFETs are used with the two PIOs for V
CC
attach
and detach. The attach and detach steps are listed below. The USB interface
transfers data at up to 12 Mbps. The schematic for the USB interface is shown in
Figure 2-8.
Attach
1. Am186CC microcontroller polls USB_Detect (PIO42) for logic High to detect
when an active host USB port is connected.
2. Am186CC microcontroller drives USB_Vcc (PIO43) High to enable Q1 and
pulls up the USBD+ line to indicate to the host that this is a full-speed device.
Detach
1. Am186CC microcontroller polls USB_Detect for logic Low to detect a
disconnect of the host.
2. Am186CC microcontroller three-states USBD± in response to a disconnect.
3. Am186CC microcontroller removes USB_V
CC
to disable Q1; Q2 isolates
USB_Detect in response to a disconnect.
Figure 2-8. ISDN TA USB Interface
PIO - USB_Detect
PIO - USB_Vcc
D-
D+
VCC3
FB3
FB2
MURATABLM21A121SPB
GS
D
Q1
TN0200T
1
32
GS
D
Q2
TN0200T
SOT-23
1
32
U14A
74ACT04
1 2
14
7
D1
DIODE RB400D
2 3
C54
22pF
C53
22pF
C52
0.1uF
R27
1.5K
R28 0
R29 0
R107
100k
P3
USB CON
AM P 787780-1
1
3
2
4
5
6
VUSB
USBD+
USBD-
GND
GND
GND
PIO42
PIO43
USBD-
USBD+
RESOUT
RESOUT#
about.book Page 11 Friday, December 18, 1998 9:41 AM