PIC18F2455-I/SP Microchip Technology Inc., PIC18F2455-I/SP Datasheet - Page 60

• Manufacturer Part Number: PIC18F2455-I/SP
• Description: Microcontroller; 24 KB Flash; 2048 RAM; 256 EEPROM; 24 I/O; 28-Pin-SPDIP
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F2455-I/SP

• A/d Inputs: 10-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 12 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 23
• Interface: I2C/SPI/USART/USB
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 28-pin SPDIP
• Programmable Memory: 24K Bytes
• Ram Size: 2K Bytes
• Speed: 48 MHz
• Timers: 1-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

PIC18F2450/4450
5.2.3
The program memory is addressed in bytes.
Instructions are stored as two bytes or four bytes in
program memory. The Least Significant Byte of an
instruction word is always stored in a program memory
location with an even address (LSb = 0). To maintain
alignment
increments in steps of 2 and the LSb will always read
‘0’ (see Section 5.1.1 “Program Counter”).
Figure 5-4 shows an example of how instruction words
are stored in the program memory.
FIGURE 5-4:
5.2.4
The standard PIC18 instruction set has four two-word
instructions: CALL, MOVFF, GOTO and LSFR. In all
cases, the second word of the instructions always has
‘1111’ as its four Most Significant bits; the other 12 bits
are literal data, usually a data memory address.
The use of ‘1111’ in the 4 MSbs of an instruction
specifies a special form of NOP. If the instruction is
executed in proper sequence, immediately after the
first word, the data in the second word is accessed and
EXAMPLE 5-4:
DS39760A-page 58
CASE 1:
Object Code
CASE 2:
Object Code
0110 0110 0000 0000
1100 0001 0010 0011
1111 0100 0101 0110
0010 0100 0000 0000
0110 0110 0000 0000
1100 0001 0010 0011
1111 0100 0101 0110
0010 0100 0000 0000
INSTRUCTIONS IN PROGRAM
MEMORY
TWO-WORD INSTRUCTIONS
with
instruction
Instruction 1:
Instruction 2:
Instruction 3:
INSTRUCTIONS IN PROGRAM MEMORY
TWO-WORD INSTRUCTIONS
Source Code
TSTFSZ
MOVFF
Source Code
TSTFSZ
ADDWF
ADDWF
MOVFF
boundaries,
Program Memory
Byte Locations
MOVLW
GOTO
MOVFF
Advance Information
REG1
REG1, REG2 ; No, skip this word
REG3
REG1
REG1, REG2 ; Yes, execute this word
REG3
055h
0006h
123h, 456h
the
PC
; is RAM location 0?
; Execute this word as a NOP
; continue code
; is RAM location 0?
; 2nd word of instruction
; continue code
LSB = 1
program
The CALL and GOTO instructions have the absolute
instruction. Since instructions are always stored on word
boundaries, the data contained in the instruction is a
word address. The word address is written to PC<20:1>,
which accesses the desired byte address in program
memory. Instruction #2 in Figure 5-4 shows how the
instruction, GOTO 0006h, is encoded in the program
memory. Program branch instructions, which encode a
relative address offset, operate in the same manner. The
offset value stored in a branch instruction represents the
number of single-word instructions that the PC will be
offset by. Section 19.0 “Instruction Set Summary”
provides further details of the instruction set.
used by the instruction sequence. If the first word is
skipped for some reason and the second word is
executed by itself, a NOP is executed instead. This is
necessary for cases when the two-word instruction is
preceded by a conditional instruction that changes the
PC. Example 5-4 shows how this works.
EFh
C1h
0Fh
F0h
F4h
Note:
memory
See Section 5.5 “Program Memory and
the Extended Instruction Set” for
information on two-word instruction in the
extended instruction set.
LSB = 0
55h
03h
00h
23h
56h
address
Word Address
© 2006 Microchip Technology Inc.
00000Ah
00000Ch
00000Eh
000000h
000002h
000004h
000006h
000008h
000010h
000012h
000014h
embedded
into
the