PIC16F-ESLASHSS datasheet(114/178 Pages) MICROCHIP

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PIC16F627A/628A/648A

DS40044F-page 112

14.11 In-Circuit Serial Programming™

(ICSP™)

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

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 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 (VPP) pin from VIL to VIHH. See “PIC16F627A/

628A/648A

EEPROM

Memory

Programming

Specification” (DS41196) for details. 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 “PIC16F627A/628A/648A

EEPROM

Memory

Programming

Specification”

(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

microcontroller to be programmed via ICSP using only

a 5V source. This mode removes the requirement of

VIHH to be placed on the MCLR pin. The LVP bit is

normally erased to ‘1’ which enables the low-voltage

programming. 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 High-Voltage Programming mode is still

available by placing VIHH 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,

VIHH must be placed onto MCLR during programming.

The LVP bit may only be programmed when program-

ming is entered with VIHH 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

VDD

VSS

RA5/MCLR/VPP

RB6/PGC

RB7/PGD

+5V

VPP

CLK

Data I/O

VDD

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

longer be used as a general purpose I/O

pin.

2: VDD must be 5.0V +10% during erase

operations.

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