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Serving Two PICs On The Same Board

Dual connection

It is possible to use single NSDSP chip to program and debug two different PICs located on the same board. To accomplish this, PGC/PGD pins are shared. MCLR pin of one of the PICs connects to the NSDSP as usual, but the second PIC's MCLR connects to AMCLR pin. Either PIC can be programmed or debugged, but not both at the same time.

NSDSP must be configured to use PGM/RTS/AMCLR pin as AMCLR. Therefore, dual-chip setup cannot be used with some older PICs which require PGM pin. It also impossible to use UART flow control with dual-chip setup.

PICs may belong to different families, but must run at the same voltage.

To enable programming and debugging, MCLR, PGC, and PGD pins must be connected. Also 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.


PGC and 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.

To ensure that one of the PICs does not interfere with programming and debugging of the other, PIC's PGC and PGD pins cannot be used for any other purpose and must be configured as inputs on both PICs.


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 1kΩ (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.


UART pins

Only one of the two PICs can communicate with the host computer's USB through UART. RX and TX pins must be connected as shown. Also 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 is not powered, the state of TX pin is undefined. Your UART module may interprete this as a beginning of transmission. To prevent this, 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.

UART flow control cannot be used. Connect the unused CTS pin to ground.

For more details on UART communicatons, click here


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

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