EPM900: Configuring for the External Clock

Information in this article applies to:

• EPM900 LPC Emulator

QUESTION

The external clock is not working with the EPM900 board. What am I doing wrong?

ANSWER

There are several things you must check to ensure you have properly configured your device.

Configuring the Keil IDE

1. Go to Project - Options for Target - Debug Tab
2. Select "LPC/EPM900 Emulator Programmer"
3. Select the Settings button
4. Change the Oscillator from Internal RC Oscillator to the selected external oscillator. Which oscillator you select depends on your design criteria.

From the P89LPC932 Data Sheet:

• Low Speed Oscillator Option - This option supports an external crystal in the range of 20 kHz to 100 kHz. Ceramic resonators are also supported in this configuration.
• Medium Speed Oscillator Option - This option supports an external crystal in the range of 100 kHz to 4 MHz. Ceramic resonators are also supported in this configuration.
• High Speed Oscillator Option - This option supports an external crystal in the range of 4 MHz to 12 MHz. Ceramic resonators are also supported in this configuration.
• External Clock Input Option - In this configuration, the processor clock is derived from an external source driving the XTAL1 / P3.1 pin. The rate may be from 0 Hz up to 12 MHz.

More than likely you will be using the Crystal (High Freq) option.

Configuring the EPM900 Board

The 12 MHz crystal on the board is not connected to the P89LPC932 bond out chip; it is used to control the functionality of the board. If you wish to use an external clock, you will have to place your own crystal at the spot marked "user XTAL" next to the "XTAL" jumpers. The capacitors on the board (c8, c9) are 22nF, and are suited for High Frequency crystals.

You must move the XTAL jumpers from INT to EXT in order to use the additional crystal you placed on the board.

You can only use the external crystal during emulation, not during programming.

MORE INFORMATION

• Refer to Configuring the Project in the EPM900 User's Guide.
• Refer to Configuring the EPM900 in the EPM900 User's Guide.

SEE ALSO

• EPM900: Problem with Programming/Emulation Mode Switch

Last Reviewed: Thursday, February 25, 2021