12C508 datasheet(46/113 Pages) MICROCHIP

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PIC12C5XX

DS40139E-page 46

8.12

In-Circuit Serial Programming

The PIC12C5XX microcontrollers with EPROM pro-

gram memory 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 cus-

tomers 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 pro-

grammed.

The device is placed into a program/verify mode by

holding the GP1 and GP0 pins low while raising the

MCLR (VPP) pin from VIL to VIHH (see programming

specification). GP1 becomes the programming clock

and GP0 becomes the programming data. Both GP1

and GP0 are Schmitt Trigger inputs in this mode.

After reset, a 6-bit command is then supplied to the

device. Depending on the command, 14-bits of pro-

gram 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 PIC12C5XX Programming Specifications.

A typical in-circuit serial programming connection is

shown in Figure 8-16.

FIGURE 8-16: TYPICAL IN-CIRCUIT SERIAL

PROGRAMMING

CONNECTION

External

Connector

Signals

To Normal

Connections

To Normal

Connections

PIC12C5XX

VDD

VSS

MCLR/VPP

GP1

GP0

+5V

VPP

CLK

Data I/O

VDD

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