Datasheet

PIC24FJXXXGA0XX
DS39768D-page 12 © 2008 Microchip Technology Inc.
3.0 DEVICE PROGRAMMING – ICSP
ICSP mode is a special programming protocol that
allows you to read and write to PIC24FJXXXGA0XX
device family memory. The ICSP mode is the most
direct method used to program the device; note, how-
ever, that Enhanced ICSP is faster. ICSP mode also
has the ability to read the contents of executive
memory to determine if the programming executive is
present. This capability is accomplished by applying
control codes and instructions, serially to the device,
using pins, PGCx and PGDx.
In ICSP mode, the system clock is taken from the
PGCx pin, regardless of the device’s oscillator Config-
uration bits. All instructions are shifted serially into an
internal buffer, then loaded into the Instruction Register
(IR) and executed. No program fetching occurs from
internal memory. Instructions are fed in 24 bits at a
time. PGDx is used to shift data in and PGCx is used
as both the serial shift clock and the CPU execution
clock.
3.1 Overview of the Programming
Process
Figure 3-1 shows the high-level overview of the
programming process. After entering ICSP mode, the
first action is to Chip Erase the device. Next, the code
memory is programmed, followed by the device
Configuration registers. Code memory (including the
Configuration registers) is then verified to ensure that
programming was successful. Then, program the
code-protect Configuration bits, if required.
FIGURE 3-1: HIGH-LEVEL ICSP™
PROGRAMMING FLOW
3.2 ICSP Operation
Upon entry into ICSP mode, the CPU is Idle. Execution
of the CPU is governed by an internal state machine. A
4-bit control code is clocked in using PGCx and PGDx,
and this control code is used to command the CPU (see
Table 3-1).
The SIX control code is used to send instructions to the
CPU for execution, and the REGOUT control code is
used to read data out of the device via the VISI register.
TABLE 3-1: CPU CONTROL CODES IN
ICSP™ MODE
Note: During ICSP operation, the operating
frequency of PGCx must not exceed
10 MHz.
4-Bit
Control Code
Mnemonic Description
0000b SIX Shift in 24-bit instruction
and execute.
0001b REGOUT Shift out the VISI (0784h)
register.
0010b-1111b N/A Reserved.
Start
Perform Chip
Erase
Program Memory
Verify Program
Done
Enter ICSP™
Program Configuration Bits
Verify Configuration Bits
Exit ICSP