Embedded System Spring, 2011 Lecture 4: The PIC Microcontrollers Eng. Wazen M. Shbair

2 IUG- Embedded System Today’s Lecture  The WREG Register  The PIC File Register

3 The WREG Register  Many registers for arithmetic and logic operation.  The WREG (WORking Register) Register is one of the most widely used registers of the PIC 8-bit register  any data larger than 8 bits must be broken into 8-bits chunks before it is processed. There is only one. 3-3 D7D6D5D2D4D3D1D0

4 MOVLW  Moves 8-bit data into WREG MOVLW k; move literal value k into WREG  Example MOVLW 25H MOVLW A5H  Is the following code correct? MOVLW 9H MOVLW A23H 1-4

5 ADDLW r ADDLW k; Add literal value k to WREG (k +WREG) r Example: r MOVLW 12H r ADDLW 16H

6 PIC WREG and ALU Using Literal Value

7 The WREG Register  When programming the WREG of PIC, the following points should be noted: Values can be loaded directly into the WREG. If values 0 to F are moved into an 8-bit register such as WREG, the rest of the bits are assumed to be all zeros. Moving a value larger than 255 (FF in hex) into the WREG register will truncate the upper byte and cause a warning in the.err file.

8 The WREG Register  MOVLW 7F2H; Illegal, becomes F2H  MOVLW 456H ; Illegal, becomes 56H  MOVLW 60A5H; Illegal, becomes A5H

9 The PIC File Register  It is the data memory. Read/Write  Static RAM Used for data storage, scratch pad and registers for internal use and function 8-bit width PIC File Register General Purpose RAM GP RAMEEPROM Special Function Registers

Register File Concept Data Bus d Decoded Instruction from Program Memory: Arithmetic/Logic Function to be Performed Result Destination Address of Second Source Operand  Register File Concept: All of data memory is part of the register file, so any location in data memory may be operated on directly  All peripherals are mapped into data memory as a series of registers  Orthogonal Instruction Set: ALL instructions can operate on ANY data memory location wf wf ALU WREG Data Memory (Register File) 07h 08h 09h 0Ah 0Bh 0Ch 0Dh 0Eh 0Fh 10h Opcode d d a a Address

11 Special Function Registers  Dedicated to specific functions such as ALU status, timers, serial communication, I/O ports, ADC,…  The function of each SFR is fixed by the CPU designer at the time of design it is used for control of the microcontroller or peripheral  8-bit registers  Their numbers varies from one chip to another. 1-11

12 General Purpose RAM  Group of RAM locations  8-bit registers  Larger than SFR Difficult to manage them by using Assembly language Easier to handle them by C Compiler.  The microchip website provides the data RAM size, which is the same as GPR size.

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Figure 2-2. File Registers of PIC12, PIC16, and PIC18

15 GP RAM vs. EEPROM in PIC chips  GPRs are used by the CPU for internal data storage.  EEPROM are considered as add-on memory that one can add externally to the ship.  So PIC chip may have zero byte of EEPROM data memory, but impossible for a PIC have zero size for the file register.

16 File Register and access bank in the PIC18  The PIC18 Family can have a max. of 4096 Bytes.  The File Register has addresses of 000- FFFH divided into 256-byte banks Max. 16 banks (How?)  At least there is one bank Known as default access bank.  Bank switching is a method used to access all the banks. 1-16

17 Access bank in the PIC18  It is 256-Byte bank.  Divided into equal two discontinuous sections (each 128 B). GP RAM, from 0 to 7FH SFR, from F80H to FFFH 1-17

18 SFRs of the PIC18 Family.

19 IUG- Embedded System19 References  Jie Hu, ECE692 Embedded Computing Systems, Fall  PIC Microcontroller And Embedded Systems: using Assembly and C for PIC 18, M. Mazidi, R. McKinlay and D. Causey, Prentice Fall,  Eng. Husam Alzaq, Embedded System Course, IUG, 2010