PIC18F45K20-E/P Microchip Technology, PIC18F45K20-E/P Datasheet - Page 14

• Manufacturer Part Number: PIC18F45K20-E/P
• Description: 32KB, Flash, 1536bytes-RAM, 36I/O, 8-bit Family,nanowatt XLP 40 PDIP .600in TUBE
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F45K20-E/P

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 48MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, HLVD, POR, PWM, WDT
• Number Of I /o: 35
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 1.5K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 3.6 V
• Data Converters: A/D 14x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: DM240313 - BOARD DEMO 8BIT XLPAC164112 - VOLTAGE LIMITER MPLAB ICD2 VPPDM164124 - KIT STARTER FOR PIC18F4XK20
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PICkit™ 3 Debug Express
DS41370C-page 10
2.2.1
Data memory is called “file register” memory in the PIC18XXXX family. It consists of up
to 4096 bytes of 8-bit RAM. Upon power-up, the values in data memory are random.
Data is organized in banks of 256 bytes, requiring that a bank (the upper 4 bits of the
register address) be selected with the Bank Select Register (BSR). Special areas in
Bank 0 and in Bank 15 can be accessed directly without concern for banking. These
special data areas are called Access RAM. The high Access RAM area is where most
of the Special Function Registers are located.
When using MPLAB C Compiler, this banking is usually transparent, but the use of the
#pragma varlocate directive tells the compiler where variables are stored, resulting
in more efficient code.
Uninitialized data memory variables, arrays and structures are usually stored in
memory with the section attribute, udata. Initialized data can be defined in MPLAB C
Compiler so that variables will have correct values when the compiler initialization
executes. This means that the values are stored in program memory, then moved to
data memory on start-up. Depending upon how much initialized memory is required for
the application, the use of initialized data (rather than simply setting the data values at
run time) may adversely affect the efficient use of program memory. Since file registers
are 8 bits, when using variables consideration should be made on what is the best
datatype to define them as. For example, when a variable value is not expected to
exceed 255, defining it as a char instead of an int will result in smaller, faster code.
2.2.2
Special Function Registers (SFRs) are CPU core registers (such as the Stack Pointer,
STATUS register and Program Counter) and include the registers for the peripheral
modules on the microprocessor. The peripherals include such things as input and
output pins, timers, USARTs and registers to read and write the EEDATA areas of the
device. MPLAB C Compiler can access these registers by name, and they can be read
and written like a variable defined in the application. Use caution, though, because
some of the Special Function Registers have characteristics different from variables.
Some have only certain bits available, some are read-only and some may affect other
registers or device operation when accessed. These registers are mapped to
addresses in Bank 15 of the data memory.
2.2.3
CALL and RETURN instructions push and pop the Program Counter on the return
address stack. The return stack is a separate area of memory, allowing 31 levels of
subroutines.
The CALL/RETURN stack is distinct from the software stack maintained by MPLAB C
Compiler. The software stack is used for automatic parameters and local variables and
resides in file register memory as defined in the Linker Script.
Data Memory
Special Function Registers
Return Address Stack
© 2009 Microchip Technology Inc.