User manual

PICDEM™ PIC18 Explorer Demonstration Board User’s Guide

2.3.2 Varying the Device Voltage (5V/3.3V)

By default, the PICDEM PIC18 Explorer Demonstration Board’s VDD supply is 5V. The

DD can be varied, for PIM-mounted microcontrollers, from 5 to 3.3V to accommodate

devices running at 5 or 3.3V. This V

DD is named VAR.

The PICDEM PIC18 Explorer Demonstration Board enables the voltage change with

PIM connection headers and a variable voltage regulator. PIMs mounted with 3.3V

devices implement the voltage change through two resistors with values that produce

the desired voltage. (See “Calculating Other V

DD Values” on page 15.)

The voltage varying hardware includes:

• An adjustable voltage regulator, the LM317 – Located on the board, left of the PIM

connectors and marked as U2 (recognizable by the TO-220 package commonly

used for transistors)

• Header J2 – Located above the PIM connectors

• Resistors R25 and R26 – Located below jumper J13

• Resistors R101 and R102 – Located on the PIM board

In setting the board’s voltage:

• For the default, 5V voltage –

- For board-mounted PIC18F8722 device:

• Board resistor R25 = 1 kΩ

• Board resistor R26 = 330Ω

- For a PIM-mounted, 5V microcontroller:

• Board resistors R25 and R26 – Same values of 1 kΩ and 330Ω,

respectively

• PIM-mounted resistors R101 and R102 – Unpopulated

• For 3.3V V

DD (achieved only with a PIM with a mounted 3.3V device, such as the

PIC18F87J11) –

- Header J2 goes into the PIM board where resistors R101 and R102 are

inserted in parallel to the board resistors R25 and R26

- PIM board resistor R101 can be unpopulated

- PIM board resistor R102 can be 1.18 kΩ.

Note: For precise adjustment of V

DD, 1% resistors are recommended.