PIC16F87 datasheet(7/24 Pages) MICROCHIP

7 / 24 page

 2002 Microchip Technology Inc.

DS39607B-page 7

PIC16F87/88

3.4

Program Mode

Program mode is entered by holding pins RB6 and RB7

low, while raising MCLR pin from VIL to VIHH (high

voltage). In this mode, the state of the RB3 pin does not

effect programming. Low-Voltage ICSP Programming

mode is entered by raising RB3 from VIL to VDD, and

then applying VDD to MCLR. Once in this mode, the

user program memory, as well as the configuration

memory, can be accessed and programmed in serial

fashion. The mode of operation is serial, and the

memory accessed is the user program memory. RB6

and RB7 are Schmitt Trigger inputs in this mode.

The sequence that enters the device into the

Programming mode places all other logic into the

RESET state (the MCLR pin was initially at VIL). This

means all I/O are in the RESET state (high-impedance

inputs).

A device RESET will clear the PC and set the address

to ‘0’. The ‘Increment Address’ command will

increment the PC. The ‘Load Configuration’ command

will set the PC to 0x2000. The available commands are

shown in Table 3-1.

The normal sequence for programming four program

memory words at a time is as follows:

Set pointer to row location.

Issue a ‘Begin Erase’ command.

Wait tprog2.

Issue an ‘End Programming’ command.

Load a word at the current program memory

address using the ‘Load Data’ command.

Issue an ‘Increment Address’ command.

Load a word at the current program memory

address using the ‘Load Data’ command.

Repeat Step 6 and Step 7 two times.

Issue a ‘Begin Programming’ command to begin

programming.

10. Wait tprog1.

11. Issue an ‘End Programming’ command.

12. Increment to the next address.

13. Repeat steps 5 through 12 seven times to

program one row.

The address and program counter are reset to 0x0000

by resetting the device (taking MCLR below VIL) and

re-entering

Programming

mode.

Program

and

configuration memory may then be read or verified

using the ‘Read Data’ and ‘Increment Address’

commands.

3.4.1

LOW-VOLTAGE ICSP

PROGRAMMING MODE

Low-voltage ICSP Programming mode allows a

PIC16F87/88 device to be programmed using VDD

only. However, when this mode is enabled by a

configuration bit (LVP), the PIC16F87/88 device

dedicates RB3 to control entry/exit into Programming

mode.

When the LVP bit is set to ‘1’, the Low-voltage ICSP

Programming entry is enabled. Since the LVP

configuration

bit

allows

Low-voltage

ICSP

Programming entry in its erased state, an erased

device will have the LVP bit enabled at the factory.

While LVP is ‘1’, RB3 is dedicated to Low-voltage ICSP

Programming. The following LVP steps assume the

LVP bit is set in the Configuration register.

Apply VDD to the VDD pin.

Drive MCLR low.

Apply VDD to the RB3/PGM pin.

Apply VDD to the MCLR pin.

All other specifications for High-voltage ICSP apply.

To disable Low-voltage ICSP mode, the LVP bit must

be programmed to ‘0’. This must be done while entered

with the High-voltage Entry mode (LVP bit = 1). RB3 is

now a general purpose I/O pin.

Note:

The Osc must not have 72 osc clocks

while the device MCLR is between VIL and

VIHH.

Note:

The MCLR pin should be raised from

below VIL to above the minimum VIHH

(VPP), within 250 µs of VDD rise. This

ensures that the device always enters

Programming

mode

before

any

instructions that may be in program

memory can be executed. Otherwise,

unintended instruction execution could

occur when the INTRC clock source is

configured as the primary clock. Refer to

Figure 7-1.

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