PIC16F688 Datasheet, PDF (119/174 Pages) Microchip Technology – 14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

11.9 Code Protection
If the code protection bit(s) have not been
programmed, the on-chip program memory can be
read out using ICSP for verification purposes.
Note:
The entire data EEPROM and Flash
program memory will be erased when the
code protection is turned off. See the
“PIC12F6XX/16F6XX Memory Program-
ming Specification” (DS41204) for more
information.
11.10 ID Locations
Four memory locations (2000h-2003h) are designated
as ID locations where the user can store checksum or
other code identification numbers. These locations are
not accessible during normal execution but are
readable and writable during Program/Verify mode.
Only the Least Significant 7 bits of the ID locations are
used.
11.11 In-Circuit Serial Programming
The PIC16F688 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 micro-
controller 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 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 11-11.
PIC16F688
FIGURE 11-11:
TYPICAL IN-CIRCUIT
SERIAL PROGRAMMING
CONNECTION
External
Connector
Signals
+5V
0V
VPP
CLK
Data I/O
To Normal
Connections
*
PIC16F688
VDD
VSS
MCLR/VPP/RA3
RA1
RA0
***
To Normal
Connections
* Isolation devices (as required)
 2004 Microchip Technology Inc.
Preliminary
DS41203B-page 117