
USB2SERA10 Data Sheet, Rev. 2
Pins and Connections
Freescale Semiconductor
6
1.4
Signals description
1.5
Power (VDD, VSS, VSSOSC, VUSB33)
The VDD and VSS are the primary power supply pins for the USB2SER. This voltage source supplies power to all the I/O buffer
circuitry and to an internal voltage regulator.
Typically, application systems have two separate capacitors across the power pins. A 10 F tantalum capacitor which provides
bulk charge storage for the overall system and a 0.1 F ceramic bypass capacitor to suppress high-frequency noise is located as
near as possible to the paired VDD and VSS power pins. The USB2SER has a VSSOSC pin. This pin must be connected to the
system ground plane or to the primary VSS pin through a low-impedance connection.
If using an external 3.3 V regulator as an input to VUSB33, the supply voltage, VDD, must not fall below the input voltage at
the VUSB33 pin. If using the internal 3.3 V regulator, do not connect an external supply to the VUSB33 pin. In this case, VDD
Table 1. Signal descriptions
Pin Number
Pin Name
Description
1
/RESUME
Pin to request a remote wake-up
2
/RESET
Reset pin
3
/SUSPEND
Indicates when the device is in suspended mode
4
NC
No connect
5
USB_LED
USB activity LED connection
6
NC
No connect
7
UART_LED
UART Activity LED connection
8
RS485_TXEN
Transmitter control pin for RS485 transceiver
9
RTS
UART request to send connect to CTS when harware flow control is
no being used.
10
CTS
UART clear to send connect to RTS when harware flow control is no
being used.
11
VDD
Supply voltage
12
NC
No connect
13
VSS
0 V ground input
14
USBDN
USB data minus signal
15
USBDP
USB data plus signal
16
VUSB33
Bidirectional signal connected to the 3.3 V regulator
17
VUSB33MON
USB Internal regulator monitor pin. Connect to VUSB33
18
NC
No connect
19
RXD
UART reception pin
20
TXD
UART transmission pin
21
XTAL
XTAL crystal oscillator pin for Pierce oscillator
22
EXTAL
EXTAL crystal oscillator pin for Pierce oscillator
23
VSS_OSC
0 V ground input for the oscillator reference
24
NC
No connect