Datasheet

 2012-2013 Microchip Technology Inc. DS60001185C-page 29
PIC32MX330/350/370/430/450/470
2.5 ICSP Pins
The PGECx and PGEDx pins are used for In-Circuit
Serial Programming™ (ICSP™) and debugging pur
-
poses. 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 recommended, with the value in the range of a few
tens of Ohms, not to exceed 100 Ohms.
Pull-up resistors, series diodes and capacitors on the
PGECx and PGEDx pins are not recommended as they
will interfere with the programmer/debugger communi
-
cations to the device. If such discrete components are
an application requirement, they should be removed
from the circuit during programming and debugging.
Alternatively, 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
(V
IH) and input low (VIL) requirements.
Ensure that the “Communication Channel Select” (i.e.,
PGECx/PGEDx pins) programmed into the device
matches the physical connections for the ICSP to
MPLAB
®
ICD 3 or MPLAB REAL ICE™.
For more information on ICD 3 and REAL ICE
connection requirements, refer to the following
documents that are available on the Microchip web
site.
• “Using MPLAB
®
ICD 3” (poster) DS50001765
• “MPLAB
®
ICD 3 Design Advisory” DS50001764
• “MPLAB
®
REAL ICE™ In-Circuit Debugger
User’s Guide” DS50001616
• “Using MPLAB
®
REAL ICE™ Emulator” (poster)
DS50001749
2.6 JTAG
The TMS, TDO, TDI and TCK pins are used for testing
and debugging according to the Joint Test Action
Group (JTAG) standard. It is recommended to keep the
trace length between the JTAG connector and the
JTAG pins on the device as short as possible. If the
JTAG connector is expected to experience an ESD
event, a series resistor is recommended, with the value
in the range of a few tens of Ohms, not to exceed 100
Ohms.
Pull-up resistors, series diodes and capacitors on the
TMS, TDO, TDI and TCK pins are not recommended
as they will interfere with the programmer/debugger
communications to the device. If such discrete compo
-
nents are an application requirement, they should be
removed from the circuit during programming and
debugging. Alternatively, refer to the AC/DC character-
istics and timing requirements information in the
respective device Flash programming specification for
information on capacitive loading limits and pin input
voltage high (V
IH) and input low (VIL) requirements.
2.7 Trace
The trace pins can be connected to a hardware
trace-enabled programmer to provide a compressed
real-time instruction trace. When used for trace, the
TRD3, TRD2, TRD1, TRD0 and TRCLK pins should
be dedicated for this use. The trace hardware
requires a 22 Ohm series resistor between the trace
pins and the trace connector.
2.8 External Oscillator Pins
Many MCUs have options for at least two oscillators: a
high-frequency primary oscillator and a low-frequency
secondary oscillator (refer to
Section 8.0 “Oscillator
Configuration” for details).
The oscillator circuit should be placed on the same side
of the board as the device. Also, place the oscillator cir
-
cuit close to the respective oscillator pins, not exceed-
ing one-half inch (12 mm) distance between them. The
load capacitors should be placed next to the oscillator
itself, on the same side of the board. Use a grounded
copper pour around the oscillator circuit to isolate them
from surrounding circuits. The grounded copper pour
should be routed directly to the MCU ground. Do not
run any signal traces or power traces inside the ground
pour. Also, if using a two-sided board, avoid any traces
on the other side of the board where the crystal is
placed. A suggested layout is illustrated in
Figure 2-3.
FIGURE 2-3: SUGGESTED OSCILLATOR
CIRCUIT PLACEMENT
2.9 Unused I/Os
Unused I/O pins should not be allowed to float as
inputs. They can be configured as outputs and driven
to a logic-low state.
Alternatively, inputs can be reserved by connecting the
pin to V
SS through a 1k to 10k resistor and configuring
the pin as an input.
Main Oscillator
Guard Ring
Guard Trace
Secondary
Oscillator