PIC12F635ESS datasheet(149/234 Pages) MICROCHIP

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DS41232D-page 147

PIC12F635/PIC16F636/639

12.15 In-Circuit Serial Programming

The PIC12F635/PIC16F636/639 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

• 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

firmware to be programmed.

The device is placed into a Program/Verify mode by hold-

ing the RA0 and RA1 pins low, while raising the MCLR

(VPP) pin from VIL to VIHH. See the “PIC12F6XX/16F6XX

Memory Programming Specification” (DS41204) for

more information. RA0 becomes the programming data

and RA1 becomes the programming clock. Both RA0

and RA1 are Schmitt Trigger inputs in this mode.

After Reset, to place the device into Program/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 on

whether the command was a load or a read. For

complete details of serial programming, please refer to

the

“PIC12F6XX/16F6XX

Memory

Programming

Specification” (DS41204).

A typical In-Circuit Serial Programming connection is

shown in Figure 12-11.

FIGURE 12-11:

TYPICAL IN-CIRCUIT

SERIAL PROGRAMMING

CONNECTION

12.16 In-Circuit Debugger

Since in-circuit debugging requires the loss of clock,

data and MCLR pins, MPLAB® ICD 2 development with

a 14-pin device is not practical. A special 20-pin

PIC16F636 ICD device is used with MPLAB ICD 2 to

provide separate clock, data and MCLR pins and frees

all normally available pins to the user.

Use of the ICD device requires the purchase of a

special header. On the top of the header is an

MPLAB ICD 2 connector. On the bottom of the

header is a 14-pin socket that plugs into the user’s

target via the 14-pin stand-off connector.

When the ICD pin on the PIC16F636 ICD device is held

low, the In-Circuit Debugger functionality is enabled.

This function allows simple debugging functions when

used with MPLAB ICD 2. When the microcontroller has

this feature enabled, some of the resources are not

available for general use. Table 12-9 shows which

features are consumed by the background debugger:

TABLE 12-9:

DEBUGGER RESOURCES

For more information, see the “MPLAB® ICD 2 In-Circuit

Debugger User’s Guide” (DS51331), available on

Microchip’s web site (www.microchip.com).

FIGURE 12-12:

20-PIN ICD PINOUT

External

Connector

Signals

To Normal

Connections

To Normal

Connections

PIC16F636

VDD

VSS

MCLR/VPP/RA3

RA1

RA0

+5V

VPP

CLK

Data I/O

*Isolation devices (as required).

Resource

Description

I/O pins

ICDCLK, ICDDATA

Stack

1 level

Program Memory

Address 0h must be NOP

700h-7FFh

20-Pin PDIP

In-Circuit Debug Device

ICDMCLR/VPP

VDD

RA5

RA4

RA3

ICDCLK

ICDDATA

VSS

RA0

ICD

RA1

RA2

RC5

RC4

RC3

RC0

RC1

RC2

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