© 1998 Microchip Technology Inc.

DS91026A-page 1

M

INTRODUCTION

Many applications require the microcontroller to cal-

culate a checksum on the program memory to deter-

mine if the contents have been corrupted. Until now,

the capability to read from program memory are the

PIC17CXXX devices. The PIC16F87X devices are

the first 14-bit core PICmicro microcontrollers that

are able to access program memory in the same

fashion as used with data EEPROM memory. These

devices are FLASH extensions of the popular

PIC16C7X family.

Table 1 shows a comparison

between the two PICmicro microcontroller families.

TABLE 1:

PIC16C7X vs. PIC16F87X

ACCESSING MEMORY

The data EEPROM and FLASH Program memory are

both accessed using the same method. An address

and/or data value are stored in Special Function Reg-

isters (SFR) and then memory is accessed using con-

trol bits in other SFRs. There are six SFRs required to

access memory:

• EECON1

• EECON2

• EEDATA

• EEDATH

• EEADR

• EEADRH

When interfacing to data EEPROM memory, the

address is stored in the EEADR register and the data is

accessed using the EEDATA register. The operation is

controlled using the EECON1 and EECON2 registers. The

register map for EECON1 is shown in Figure 1. EECON2

is not a physical register. Reading it will result in all '0's.

This register is used exclusively in the EEPROM and

FLASH write sequences.

When interfacing to FLASH program memory, the

address is stored in the EEADRH:EEADR registers and

the data is accessed using the EEDATH:EEDATA regis-

ters. Since the same set of control registers are used

to access data and program memory, the EEPGD bit

(EECON1<7>)

is used to indicate to the microcontroller

whether the operation is going to be on data memory

(EEPGD = 0) or program memory (EEPGD = 1). Refer to

Section 7.0 in the PIC16F87X data sheet (DS30292)

for more information about using the EEPROM and

FLASH memories.

Feature

PIC16C7X

PIC16C87X

Pins

28 or 40

28 or 40

Timers

33

Interrupts

11 or 12

13 or 14

Communica-

tion

PSP, USART,

Slave)

PSP, USART,

Master/Slave)

Frequency

20 MHz

20 MHz

A/D

8-bit

10-bit

CCP

22

Program Mem. 4K or 8K EPROM

4K or 8K FLASH

RAM

192 or 368 bytes

192 or 368 bytes

Data EEPROM

None

128 or 256 bytes

Other

---

In-Circuit Debugger

Author:

Rodger Richey

Microchip Technology Inc.

TB026

Calculating Program Memory Checksums Using a PIC16F87X