PIC18F2331/2431/4331/4431
2.3
Master Clear (MCLR) Pin
2.4
ICSP Pins
The MCLR pin provides two specific device
functions: Device Reset, and Device Programming
and Debugging. If programming and debugging are
The PGC and PGD pins are used for In-Circuit Serial
Programming™ (ICSP™) and debugging purposes. It
is recommended to keep the trace length between the
ICSP connector and the ICSP pins on the device as
short as possible. If the ICSP connector is expected to
experience an ESD event, a series resistor is recom-
mended, with the value in the range of a few tens of
ohms, not to exceed 100Ω.
not required in the end application,
a
direct
connection to VDD may be all that is required. The
addition of other components, to help increase the
application’s resistance to spurious Resets from
voltage sags, may be beneficial.
A
typical
configuration is shown in Figure 2-1. Other circuit
designs may be implemented, depending on the
application’s requirements.
Pull-up resistors, series diodes, and capacitors on the
PGC and PGD pins are not recommended as they will
interfere with the programmer/debugger communica-
tions to the device. If such discrete components are an
application requirement, they should be removed from
the circuit during programming and debugging. Alter-
natively, refer to the AC/DC characteristics and timing
requirements information in the respective device
Flash programming specification for information on
capacitive loading limits and pin input voltage high (VIH)
and input low (VIL) requirements.
During programming and debugging, the resistance
and capacitance that can be added to the pin must be
considered. Device programmers and debuggers drive
the MCLR pin. Consequently, specific voltage levels
(VIH and VIL) and fast signal transitions must not be
adversely affected. Therefore, specific values of R1
and C1 will need to be adjusted based on the
application and PCB requirements. For example, it is
recommended that the capacitor, C1, be isolated from
the MCLR pin during programming and debugging
operations by using a jumper (Figure 2-2). The jumper
is replaced for normal run-time operations.
For device emulation, ensure that the “Communication
Channel Select” (i.e., PGCx/PGDx pins) programmed
into the device matches the physical connections for
the ICSP to the Microchip debugger/emulator tool.
Any components associated with the MCLR pin
should be placed within 0.25 inch (6 mm) of the pin.
For more information on available Microchip
development tools connection requirements, refer to
Section 25.0 “Development Support”.
FIGURE 2-2:
EXAMPLE OF MCLR PIN
CONNECTIONS
VDD
R1
R2
MCLR
PIC18FXXXX
JP
C1
Note 1: R1 10 k is recommended. A suggested
starting value is 10 k. Ensure that the
MCLR pin VIH and VIL specifications are met.
2: R2 470 will limit any current flowing into
MCLR from the external capacitor, C, in the
event of MCLR pin breakdown, due to
Electrostatic Discharge (ESD) or Electrical
Overstress (EOS). Ensure that the MCLR pin
VIH and VIL specifications are met.
2010 Microchip Technology Inc.
DS39616D-page 27
MICROCHIP [ MICROCHIP ]
