16F628 datasheet(111/168 Pages) MICROCHIP

111 / 168 page

 2002 Microchip Technology Inc.

Preliminary

DS40044A-page 109

PIC16F627A/628A/648A

14.11 In-Circuit Serial Programming

The PIC16F627A/628A/648A microcontrollers can be

serially programmed 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 pro-

gramming voltage. This allows customers to manufac-

ture boards with unprogrammed devices and then

program the microcontroller just before shipping the

product. This also allows the most recent firmware, or

a custom firmware to be programmed.

The device is placed into a Program/Verify mode by

holding the RB6 and RB7 pins low while raising the

MCLR (V

PP) pin from VIL to VIHH (see programming

specification). RB6 becomes the programming clock

and RB7 becomes the programming data. Both RB6

and RB7 are Schmitt Trigger inputs in this mode.

After RESET, to place the device into Programming/

Verify mode, the program counter (PC) is at location

00h. A 6-bit command is then supplied to the device.

Depending on the command, 14 bits of program data

are then supplied to or from the device, depending if

the command was a load or a read. For complete

details of serial programming, please refer to the Pro-

gramming Specifications (DS41196).

A typical In-Circuit Serial Programming connection is

shown in Figure 14-18.

FIGURE 14-18:

TYPICAL IN-CIRCUIT

SERIAL PROGRAMMING

CONNECTION

14.12 Low Voltage Programming

The LVP bit of the configuration word, enables the low

voltage programming. This mode allows the microcon-

troller to be programmed via ICSP using only a 5V

source. This mode removes the requirement of V

IHH to

be placed on the MCLR pin. The LVP bit is normally

erased to '1' which enables the low voltage program-

ming. In this mode, the RB4/PGM pin is dedicated to

the programming function and ceases to be a general

purpose I/O pin. The device will enter Programming

mode when a '1' is placed on the RB4/PGM pin. The

HV Programming mode is still available by placing V

IHH

on the MCLR pin.

If Low-voltage Programming mode is not used, the LVP

bit should be programmed to a '0' so that RB4/PGM

becomes a digital I/O pin. To program the device, V

IHH

must be placed onto MCLR during programming. The

LVP bit may only be programmed when programming

is entered with V

IHH on MCLR. The LVP bit cannot be

programmed when programming is entered with RB4/

PGM.

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

to 0, only high voltage Programming mode can be used

to program the device.

External

Connector

Signals

To Normal

Connections

To Normal

Connections

PIC16F627A/628A/648A

RA5/MCLR/V

RB6/PGC

RB7/PGD

+5V

CLK

Data I/O

Note 1: While in this mode the RB4 pin can no

longer be used as a general purpose I/O

pin.

2: V

DD must be 5.0V +10% during erase

operations.

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