PIC876 datasheet(136/218 Pages) MICROCHIP

136 / 218 page

PIC16F87X

DS30292C-page 134

 2001 Microchip Technology Inc.

12.17

In-Circuit Serial Programming

PIC16F87X microcontrollers can be serially pro-

grammed while in the end application circuit. This is

simply done with two lines for clock and data and three

other lines for power, ground, and the programming

voltage. This allows customers to manufacture boards

with unprogrammed devices, and then program the

microcontroller just before shipping the product. This

also allows the most recent firmware, or a custom firm-

ware to be programmed.

When using ICSP, the part must be supplied at 4.5V to

5.5V, if a bulk erase will be executed. This includes

reprogramming of the code protect, both from an on-

state to off-state. For all other cases of ICSP, the part

may be programmed at the normal operating voltages.

This means calibration values, unique user IDs, or user

code can be reprogrammed or added.

For complete details of serial programming, please

refer to the EEPROM Memory Programming Specifica-

tion for the PIC16F87X (DS39025).

12.18 Low Voltage ICSP Programming

The LVP bit of the configuration word enables low volt-

age ICSP programming. This mode allows the micro-

controller to be programmed via ICSP using a VDD

source in the operating voltage range. This only means

that VPP does not have to be brought to VIHH, but can

instead be left at the normal operating voltage. In this

mode, the RB3/PGM pin is dedicated to the program-

ming function and ceases to be a general purpose I/O

pin. During programming, VDD is applied to the MCLR

pin. To enter Programming mode, VDD must be applied

to the RB3/PGM, provided the LVP bit is set. The LVP

bit defaults to on (‘1’) from the factory.

If Low Voltage Programming mode is not used, the LVP

bit can be programmed to a '0' and RB3/PGM becomes

a digital I/O pin. However, the LVP bit may only be pro-

grammed when programming is entered with VIHH on

MCLR. The LVP bit can only be charged when using

high voltage on MCLR.

It should be noted, that once the LVP bit is programmed

to 0, only the High Voltage Programming mode is avail-

able and only High Voltage Programming mode can be

used to program the device.

When using low voltage ICSP, the part must be supplied

at 4.5V to 5.5V, if a bulk erase will be executed. This

includes reprogramming of the code protect bits from an

on-state to off-state. For all other cases of low voltage

ICSP, the part may be programmed at the normal oper-

ating voltage. This means calibration values, unique

user IDs, or user code can be reprogrammed or added.

Note 1: The High Voltage Programming mode is

always available, regardless of the state

of the LVP bit, by applying VIHH to the

MCLR pin.

2: While in Low Voltage ICSP mode, the

RB3 pin can no longer be used as a gen-

eral purpose I/O pin.

3: When using low voltage ICSP program-

ming (LVP) and the pull-ups on PORTB

are enabled, bit 3 in the TRISB register

must be cleared to disable the pull-up on

RB3 and ensure the proper operation of

the device.

4: RB3 should not be allowed to float if LVP

is enabled. An external pull-down device

should be used to default the device to

normal operating mode. If RB3 floats

high, the PIC16F87X device will enter

Programming mode.

5: LVP mode is enabled by default on all

devices shipped from Microchip. It can be

disabled by clearing the LVP bit in the

CONFIG register.

6: Disabling LVP will provide maximum com-

patibility to other PIC16CXXX devices.

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