5.5 Special Function Pins

Name	Type	Polarity/Bus Size	Description
NC	—	—	No connect This pin is not connected to circuitry within the device. These pins can be driven to any voltage or can be left floating with no effect on the operation of the device.
DC	—	—	Do not connect. This pin should not be connected to any signals on the PCB. These pins should be left unconnected.
LPXIN	In	1	Low power 32 KHz crystal oscillator. Input from the 32 KHz oscillator. Pin for connecting a low power 32 KHz watch crystal. If not used, the LPXIN pin can be left floating. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.
LPXOUT	In	1	Low power 32 KHz crystal oscillator. Output to the 32 KHz oscillator. Pin for connecting a low power 32 KHz watch crystal. If not used, the LPXOUT pin can be left floating. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.
MAINXIN	In	1	Main crystal oscillator circuit. Input to the crystal oscillator circuit. Pin for connecting an external crystal, ceramic resonator, or RC network. When using an external crystal or ceramic oscillator, external capacitors are also recommended. Refer to documentation from the crystal oscillator manufacturer for proper capacitor value. If using an external RC network or clock input, MAINXIN should be grounded for better noise immunity. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.
MAINXOUT	Out	1	Main crystal oscillator circuit. Output from the crystal oscillator circuit. Pin for connecting external crystal or ceramic resonator. When using an external crystal or ceramic oscillator, external capacitors are also recommended. Refer to documentation from the crystal oscillator manufacturer for proper capacitor value. If using external RC network or clock input, MAINXIN should be grounded and MAINXOUT left unconnected. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.
NCAP	—	1	Negative capacitor connection. This is the negative terminal of the charge pump. A capacitor, with a 2.2 μF recommended value, is required to connect between PCAP and NCAP. Analog charge pump capacitors are not needed if none of the analog SCB features are used and none of the SDDs are used. In that case it should be left unconnected.
PCAP	—	1	Positive Capacitor connection. This is the positive terminal of the charge pump. A capacitor, with a 2.2 μF recommended value, is required to connect between PCAP and NCAP. If this pin is not used, it must be left unconnected/floating. In this case, no capacitor is needed. Analog charge pump capacitors are not needed if none of the analog SCB features are used, and none of the SDDs are used.
PTBASE	—	1	Pass transistor base connection This is the control signal of the voltage regulator. This pin should be connected to the base of an external pass transistor used with the 1.5V internal voltage regulator and can be floating if not used.
PTEM	—	1	Pass transistor emitter connection. This is the feedback input of the voltage regulator. This pin should be connected to the emitter of an external pass transistor used with the 1.5V internal voltage regulator and can be floating if not used.
MSS_RESET_N	—	Low	Low Reset signal which can be used as an external reset and can also be used as a system level reset under control of the Cortex-M3 processor. MSS_RESET_N is an output asserted low after power-on reset. The direction of MSS_RESET_N changes during the execution of the Microchip System Boot when chip-level reset is enabled. The Microchip System Boot reconfigures MSS_RESET_N to become a reset input signal when chip-level reset is enabled. It has an internal pull-up so it can be left floating. In the current software, the MSS_RESET_N is modeled as an external input signal only.
PU_N	In	Low	Push-button is the connection for the external momentary switch used to turn on the 1.5V voltage regulator and can be floating if not used.

NC

—

No connect

This pin is not connected to circuitry within the device. These pins can be driven to any voltage or can be left floating with no effect on the operation of the device.

DC

—

Do not connect.

This pin should not be connected to any signals on the PCB. These pins should be left unconnected.

LPXIN

In

1

Low power 32 KHz crystal oscillator.

Input from the 32 KHz oscillator. Pin for connecting a low power 32 KHz watch crystal. If not used, the LPXIN pin can be left floating. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.

LPXOUT

In

1

Low power 32 KHz crystal oscillator.

Output to the 32 KHz oscillator. Pin for connecting a low power 32 KHz watch crystal. If not used, the LPXOUT pin can be left floating. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.

MAINXIN

In

1

Main crystal oscillator circuit.

Input to the crystal oscillator circuit. Pin for connecting an external crystal, ceramic resonator, or RC network. When using an external crystal or ceramic oscillator, external capacitors are also recommended. Refer to documentation from the crystal oscillator manufacturer for proper capacitor value.

If using an external RC network or clock input, MAINXIN should be grounded for better noise immunity. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.

MAINXOUT

Out

1

Main crystal oscillator circuit.

Output from the crystal oscillator circuit. Pin for connecting external crystal or ceramic resonator. When using an external crystal or ceramic oscillator, external capacitors are also recommended. Refer to documentation from the crystal oscillator manufacturer for proper capacitor value.

If using external RC network or clock input, MAINXIN should be grounded and MAINXOUT left unconnected. For more information, see the PLLs, Clock Conditioning Circuitry, and On-Chip Crystal Oscillators section in the SmartFusion Microcontroller Subsystem User’s Guide.

NCAP

—

1

Negative capacitor connection.

This is the negative terminal of the charge pump. A capacitor, with a 2.2 μF recommended value, is required to connect between PCAP and NCAP. Analog charge pump capacitors are not needed if none of the analog SCB features are used and none of the SDDs are used. In that case it should be left unconnected.

PCAP

—

1

Positive Capacitor connection.

This is the positive terminal of the charge pump. A capacitor, with a 2.2 μF recommended value, is required to connect between PCAP and NCAP. If this pin is not used, it must be left unconnected/floating. In this case, no capacitor is needed. Analog charge pump capacitors are not needed if none of the analog SCB features are used, and none of the SDDs are used.

PTBASE

—

1

Pass transistor base connection

This is the control signal of the voltage regulator. This pin should be connected to the base of an external pass transistor used with the 1.5V internal voltage regulator and can be floating if not used.

PTEM

—

1

Pass transistor emitter connection.

This is the feedback input of the voltage regulator.

This pin should be connected to the emitter of an external pass transistor used with the 1.5V internal voltage regulator and can be floating if not used.

MSS_RESET_N

—

Low

Low Reset signal which can be used as an external reset and can also be used as a system level reset under control of the Cortex-M3 processor. MSS_RESET_N is an output asserted low after power-on reset. The direction of MSS_RESET_N changes during the execution of the Microchip System Boot when chip-level reset is enabled. The Microchip System Boot reconfigures MSS_RESET_N to become a reset input signal when chip-level reset is enabled. It has an internal pull-up so it can be left floating. In the current software, the MSS_RESET_N is modeled as an external input signal only.

PU_N

In

Low

Push-button is the connection for the external momentary switch used to turn on the 1.5V voltage regulator and can be floating if not used.