Developing Applications

Microstick for 3V PIC24 K Series Devices only implements circuitry for low-voltage

ICSP™ programming. To enable low-voltage ICSP programming, it is important to

always configure the microcontroller to enable MCLR pin function, rather than RA5

general purpose input pin function.

The following assembly language directive enables the MCLR pin function in the

device Configuration bits:

; MCLR Pin Enable bit (RA5 input disabled; MCLR enabled)

config __FPOR, MCLRE_ON

In C30, the same thing is accomplished with this code:

// MCLR Pin Enable bit (RA5 input disabled; MCLR enabled)

FPOR(MCLRE_ON)

The slide switch, labeled S3 on the PCB, is used to select which pair of PGECx/

PGEDx pins to use for In-Circuit Serial Programming™ (ICSP™). When moved

towards the DIP socket, the Microstick is set for using PGEC3/PGED3. When

moved towards the USB connector, the Microstick is configured for PGEC1/

PGED1.

To allow for debugging to work in MPLAB, the device’s Configuration bits must be

set up to indicate which PGECx/PGEDx pins are actually being used in the circuit.

For example, in assembly language, you may need directives such as this:

.include "p24Fxxxx.inc"

; ICD Pin Placement Select (EMUC/EMUD share PGC3/PGD3)

config __FICD, ICS_PGx3

In C30, the same thing can be accomplished with this code:

#include <p24Fxxxx.h>

// ICD Pin Placement Select (EMUC/EMUD share PGC3/PGD3)

_FICD(ICS_PGx3)

A C30 firmware source code example for blinking the Microstick’s LED is provided

Warning: Always program the microcontroller with MCLR pin functionality

enabled so that the Microstick for 3V PIC24 K Series Devices can

be used to program/debug the chip in the future.

If the microcontroller is programmed with MCLR pin function dis-

abled (RA5 input enabled), the Microstick will no longer program or

debug firmware on the microcontroller, because Microstick does

not have circuitry to use high-voltage ICSP entry. REAL ICE™,

MPLAB ICD 3 and PICkit™ 3 are an example of high-voltage ICSP

tools that can be used to recover the part.

Hardware Design

The Microstick for 3V PIC24 K Series Devices is USB bus-powered. An on-board

MCP1727 LDO regulator provides +3.3 VDC output from the USB bus power.

Turning power on/off to the target application is controlled by the MPLAB IDE via

the FPF2102 load switch. The FPF2102 load switch automatically shuts down

power to the target if the current exceeds a trip point of 200 mA to 400 mA. This

may help protect the host PC USB port from accidental shorting of power supply

pins in the target application circuit.

The Microstick may be plugged into a prototyping board to develop external appli-

pins are provided, labeled P1, P2 and P3. Normally, the skinny DIP layout

(300 mils) should be used by populating rows, P1 and P2. Optionally, rows, P1

and P3, may be populated instead to provide a wide DIP layout (600 mils). The

unpopulated, single in-line pin header for soldering into P3 is available separately

as Digi-Key Part Number ED7464-ND.

Using the 16-Bit XLP Development Board

In the skinny DIP layout configuration (rows, P1 and P2, are populated), the Micro-

stick may be plugged into Microchip’s “16-Bit XLP Development Board”. The 16-Bit

XLP Development Board provides several external buttons, LEDs, peripherals and

sensors that can be used to quickly evaluate the device without spending time

wiring a breadboard.

The 16-Bit XLP Development Board may come with a USB-to-Serial or RS-232

serial port wired to the PIC microcontroller’s U2TX/U2RX pins. To avoid conflict

with the on-board serial port circuitry, slide S3 of the Microstick to the PGEC3/

PGED3 setting (move the switch lever towards the DIP socket).

Warning: Always remove batteries and/or the “POWER SOURCE SELECT”

jumper from the 16-Bit XLP Development Board, prior to inserting

the Microstick board. The Microstick for 3V PIC24 K Series Devices

is intended to supply power to the target application, which could

cause an unintended charging of batteries connected to the 16-Bit

XLP Development Board.