Header Board Specification
WHY DO I NEED A HEADER TO DEBUG?
Some PIC microcontrollers, particularly low pin count devices (with 20 pins or less),
generally must use a header for debugging. This is done to free up I/O lines for your
application and to make production parts more affordable. Optional headers are also
available for high pin count devices (with 64 pins or higher).
Debugging requires a two-line connection (plus VDD, VSS and VPP) to communicate
with the device. In a high pin count device, losing a few I/O lines is generally not a prob-
lem for most designs. But in a low pin count device, it can be a critical problem. Imagine
having to do an 8-pin design where there are only 5 I/Os, having used up 2 I/Os just for
debugging!
Headers are also used to save you money. In high pin count devices, adding debug-
ging to the silicon can generally be done at little or no cost since the silicon is already
fairly large. However, low pin count devices are low cost specifically because they use
very little silicon. So, adding debugging circuitry on-board these parts would add sig-
nificant cost since it would raise the amount of silicon used by a considerable percent-
age. The header places the cost for debugging up front and frees your production parts
from the extra cost of an unused debug module.
Microchip also makes optional debug modules, usually for high pin count devices. The
module is optional because you can still do basic debugging without a header, but if
you use one, you get back I/O lines, and may also gain additional debugging features.
Only certain devices can use an optional header, see the device page on our website
for details.
Microchip lists what header must be ordered to work with your device, if one is required.
Simply consult the device page on our website, or our other ordering guides.
Note that in all cases, devices can be programmed in circuit (called ICSP) with very
few exceptions. Even devices without an internal debug feature can still be pro-
grammed by connecting the programming/debugging tool to the in-circuit programming
lines. These devices simply cannot perform debugging without a header.
FIGURE 1: PRODUCTION DEVICE VS. HEADER DEVICE (-ICE/-ICD)
VDD
1
20
ENABLE ICDCLK
19
2
ICDMCLR ICDDATA
3
3 18
VDD Vss
1 14
1 2
4 17
2 13
5
16
3 12
VDD Vss
6 15
4
11 JP1
14
7
5 10
13
8
9
6
12
9
7 8
10 11
ICD NC
Production Device
-ICE/-ICD Device
To Tool Connector
on Header Board
2009 Microchip Technology Inc. DS51292R-page 1Header Board Specification
DEBUG DETAILS
Next generation in-circuit emulators (such as the MPLAB REAL ICE in-circuit
emulator) and in-circuit debuggers work with devices that have on-chip debug circuitry.
Sometimes the actual production device will have this circuitry and sometimes a
special version of this device is required or available for code debugging. This special
version of the chip, with the suffix -ICD or -ICE, is mounted on a header board
(Figure 2).
Note: ICE/ICD devices are only used on the header; they are not sold separately.
FIGURE 2: DEBUG OPTIONS
Production Device without Production Device with
On-Board Debug Circuitry On-Board Debug Circuitry
Vdd Vss
Rx1/DAT
Rx0/CLK
MCLR/Vpp
Debug
Circuitry
No debug capability. Debug capability available.
Header required for debug. However, header can provide
dedicated resources for debug.
Header board with additional
ICE/ICD Device with On-board Debug
circuitry to support debug
Circuitry, Dedicated Debug Pins and
functions.
(sometimes) Dedicated Debug Memory
S1
VSS J1
VDD
DAT
MCLR CLK
VPP Rx1
Rx0
TP1
TP2
ICE/
Debug
TP3
ICD
Memory
Device
Debug
Circuitry
In general, ICE devices are designed for next-generation in-circuit emulator use and
ICD devices are designed for in-circuit debugger use. However, ICE devices may be
used with an in-circuit debugger and ICD devices may be used with a next-generation
in-circuit emulator, but will provide only basic ICD functionality.
To determine what device resources must be dedicated to debugging for either a
device with on-board debug capability or the special ICE/ICD device, see the
Resources used by ... section of the in-circuit emulator or in-circuit debugger on-line
help file.
DS51292R-page 2 2009 Microchip Technology Inc.
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