AN2690 Freescale Semiconductor / Motorola, AN2690 Datasheet

AN2690

Manufacturer Part Number

AN2690

Description

Low Frequency EEPROM Emulation on the MC68HLC908QY4

Manufacturer

Freescale Semiconductor / Motorola

Datasheet

1.AN2690.pdf (34 pages)

Current page: 1 of 34
Download datasheet (397Kb)

Application Note

AN2690

03/2004

Low Frequency EEPROM

Emulation on the

MC68HLC908QY4

By Alan Devine

Introduction

8/16-Bit Division

East Kilbride, Scotland

To avoid the cost of using external EEPROM devices, the FLASH on Motorola

microcontrollers can be used in most applications to emulate EEPROM.

Techniques for emulating EEPROM on the MC68HLC908QY4 family are

discussed in application note AN2346. These techniques require the MCU to

be running with a minimum bus frequency of 1 MHz. This application note

discusses how to emulate EEPROM on the MC68HLC908QY4 when an

external 32768 Hz crystal oscillator is used to drive the application.

As the FLASH on the device requires a minimum program bus clock frequency

of 1 MHz, the crystal clock is too slow to successfully program the FLASH

array. A potential solution is to run the device from the internal oscillator

(typically 4 MHz) when programming the FLASH, and then to switch back to the

external crystal for the main application. However, due to the security

implemented on the MC68HLC908QY family, it is possible to write to the clock

selection register (change clock source) only once after reset. Thus, in order to

switch to the internal oscillator when running on the crystal clock, a reset of the

MCU must be forced. This can be done using one of the following methods:

Illegal Opcode, Illegal Address, COP Timeout and External Reset; however,

resuming execution of the application is more difficult, as the reset vector is

fetched and all modules and registers are reset to their default state, which

could be a limitation in some applications.

Two general methods are presented; Method 1, where a reset is forced at the

beginning of the loop; and Method 2, where a reset can be forced anywhere in

the loop. The advantages and disadvantages of the two methods are listed.

Although the particular methods may not fit the specific application exactly, it

should be possible to apply one of them. Before these methods are examined,

the techniques of forcing a reset are described.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

Related parts for AN2690

Related keywords

AN2690 datasheet
AN2690 data sheet
AN2690 pdf datasheet
AN2690 component
AN2690 part
AN2690 distributor
AN2690 RoHS
AN2690 datasheet download