PIC16F627A Datasheet, PDF (111/168 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontrollers

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 (VPP) 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
External
Connector
Signals
+5V
0V
VPP
CLK
Data I/O
To Normal
Connections
PIC16F627A/628A/648A
VDD
VSS
RA5/MCLR/VPP
RB6/PGC
RB7/PGD
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 VIHH 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 VIHH
on the MCLR pin.
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.
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 programming
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.
VDD
To Normal
Connections
 2002 Microchip Technology Inc.
Preliminary
DS40044A-page 109