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Board Powered 3.3V Configuration

NSDSP based on PIC16LF1454 must be used for all 3.3V configurations

When NSDSP is powered by the board, it senses USB cable attachments and detachments with its EN pin (see pinout). EN pin must be kept low when USB cable is not attched. When USB cable attaches, EN pin must be driven to 3.3V to wake up NSDSP. This can be accomplished by using a voltage divider as shown in the schematics below (R3 and R4).

While EN pin is low, NSDSP enters sleep mode. When USB cable attaches, NSDSP wakes up and tries to initiate USB session. When USB cable gets detached, NSDSP resets and then enter sleep mode again. There's a brief moment when NSDSP is in reset. During this moment, all the NSDSP pins go into high impedance state.

Schematics

For the locations of the NSDSP pins, refer to the pinout diagram. Only PIC pins used for connecting NSDSP are shown. For the list of connections necessary to run the PIC, refer to the datasheet for your PIC device.

This schematics does not show any ESD protection devices which may or may not be needed for the application.

To enable programming and debugging, MCLR, PGC, and PGD pins must be connected. Also USB ground, NSDSP ground and PIC ground must be connected together. R1 is necessary to prevent damages to PIC or NSDSP. R2 must be at least 1kΩ. Using higher values, up to 10kΩ, will decrease power consumption during programming, but may interfere with high speed programming rates. Traces connecting PGC and PGD pins must be kept as short as possible. If longer traces are needed, it is best not to run them parallel to each other. Do not connect any diodes or capacitors to PGC or PGD pins.

If your PIC has several pairs of PGD/PGC pins, you can use any pair, but you must use it as a pair. Do not combine pins from different pairs.

 

PGC and PGD pins

PGC and PGD pins are busy during programming and debugging. However, you can use them during run time.

To use PGC and PGD as inputs, connect them to the source through resistors. Resistors must be at least 10kΩ (more if values of R1/R2 were increased above 1kΩ). Resistors must be connected directly to PIC's PGC or PGD pins, not to corresponding NSDSP's pins. Configure NSDSP to put PGC and PGD pins into the high impedance state while not in use. Otherwise NSDSP will drive these pins.

To use PGC and PGD as outputs, connect them directly or through protective resistors. Combined impendance must be at least 10kΩ (more if values of R1/R2 were increased above 1kΩ). Configure NSDSP to put PGC and PGD pins into the high impedance state while not in use. Otherwise NSDSP will drive these pins causing power dissipation through R1 or R2. Make sure that devices connected to these pins can tolerate high frequency signaling during programming or debugging.

To use PGC and PGD to detect USB state, configure NSDSP to alter the state of the pins depending on USB state. Once configured, you can read the state of these pins to detect when USB power is connected, when USB connection is established, and when NSDSP enters UART mode. However, when NSDSP transistions to low power mode, there is a brief moment when NSDSP resets. During the short time, both PGC and PGDO pins are put into high impedance state. This may lead to unpredictable results when you're trying to read the state of these pins. To make them predictable, add 100kΩ pull-down or pull-up resistors to NSDSP's PGC and PGDO pins. Connect the resistors directly to NSDSP's PGC and PGDO pins, not to corresponding PIC's pins.

If not using PGC and PGD configure them as inputs. Configure NSDSP to drive PGC and PGD pins low while not in use. If you also want to make sure these pins are not floating during short reset and start-up periods, connect 100kΩ pull-down resistors to NSDSP's PGC and PGDO pins.

 

MCLR pin

Some PIC devices require an MCLR circuit which includes capacitor to the ground and pull-up resistor (see datasheet for your PIC). If such circuit is used, isolate the circuit from the PIC's MCLR pin with 470Ω (or more) resistor, and make sure that NSDSP connects directly to the PIC's MCLR pin without any resistors in-between.

If your PIC device allows using MCLR as a GP input, you must enable MCLRE and LVP configuration bits.

 

UART pins

To communicate with the host computer through USB, your PIC can use UART. RX and TX pins must be connected as shown. Also USB ground, NSDSP ground and PIC ground must be connected together. When not in use, NSDSP drives its TX pin high at all times. However, when NSDSP resets, the TX pin enters high impedance state. Your UART module may interprete this as a beginning of transmission. To prevent the glitch, a 100kΩ pull-up resistor may be connected to NSDSP's TX pin.

If UART is not needed, leave TX pin unconnected, and connect RX to VDD.

If UART flow control is required, RTS and CTS pins must be connected too. While NSDSP is not in the UART mode with flow control, RTS pin is kept low (unless you configure NSDSP to use it as AMCLR). If flow control is not needed, leave RTS unconnected and connect CTS to ground.

For more details on UART communicatons, click here

 

There may be special considerations for your specific PIC device. Please visit the Supported Devices section, find your device and read the documentation.

To order pre-programmed NSDSP chips for 3.3V configurations, click on one of the links below.

Model Package
3.3V: PIC16LF1454 DIP SOIC SSOP QFN
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