 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
PIC18F4431 Datasheet(PDF) 65 Page - Microchip Technology |
|
||||||||||||||||||||||||||||||
PIC18F4431 Datasheet(HTML) 65 Page - Microchip Technology |
|
|
65 / 396 page  2003 Microchip Technology Inc. Preliminary DS39616B-page 63 PIC18F2331/2431/4331/4431 5.8 Look-up Tables Look-up tables are implemented two ways: • Computed GOTO • Table Reads 5.8.1 COMPUTED GOTO A computed GOTO is accomplished by adding an offset to the program counter. An example is shown in Example 5-4. A look-up table can be formed with an ADDWF PCL instruction and a group of RETLW 0xnn instructions. WREG is loaded with an offset into the table before executing a call to that table. The first instruction of the called routine is the ADDWF PCL instruction. The next instruction executed will be one of the RETLW 0xnn instructions, which returns the value 0xnn to the calling function. The offset value (in WREG) specifies the number of bytes that the program counter should advance, and should be multiples of 2 (LSB = 0). In this method, only one data byte may be stored in each instruction location and room on the return address stack is required. EXAMPLE 5-4: COMPUTED GOTO USING AN OFFSET VALUE 5.8.2 TABLE READS/TABLE WRITES A better method of storing data in program memory allows two bytes of data to be stored in each instruction location. Look-up table data may be stored two bytes per pro- gram word by using table reads and writes. The table pointer (TBLPTR) specifies the byte address and the table latch (TABLAT) contains the data that is read from, or written to program memory. Data is transferred to/from program memory, one byte at a time. The Table Read/Table Write operation is discussed further in Section 6.1 “Table Reads and Table Writes”. 5.9 Data Memory Organization The data memory is implemented as static RAM. Each register in the data memory has a 12-bit address, allowing up to 4096 bytes of data memory. Figure 5-6 shows the data memory organization for the PIC18F2331/2431/4331/4431 devices. The data memory map is divided into as many as 16 banks that contain 256 bytes each. The lower 4 bits of the Bank Select Register (BSR<3:0>) select which bank will be accessed. The upper 4 bits for the BSR are not implemented. The data memory contains Special Function Registers (SFR) and General Purpose Registers (GPR). The SFRs are used for control and status of the controller and peripheral functions, while GPRs are used for data storage and scratch pad operations in the user’s application. The SFRs start at the last location of Bank 15 (FFFh) and extend to F60h. Any remaining space beyond the SFRs in the bank may be implemented as GPRs. GPRs start at the first location of Bank 0 and grow upwards. Any read of an unimplemented location will read as ‘0’s. The entire data memory may be accessed directly or indirectly. Direct addressing may require the use of the BSR register. Indirect addressing requires the use of a File Select Register (FSRn) and a corresponding Indirect File Operand (INDFn). Each FSR holds a 12- bit address value that can be used to access any location in the Data Memory map without banking. See Section 5.12 “Indirect Addressing, INDF and FSR Registers” for indirect addressing details. The instruction set and architecture allow operations across all banks. This may be accomplished by indirect addressing or by the use of the MOVFF instruction. The MOVFF instruction is a two-word/two-cycle instruction that moves a value from one register to another. To ensure that commonly used registers (SFRs and select GPRs) can be accessed in a single cycle, regardless of the current BSR values, an Access Bank is implemented. A segment of Bank 0 and a segment of Bank 15 comprise the Access RAM. Section 5.10 “Access Bank” provides a detailed description of the Access RAM. 5.9.1 GENERAL PURPOSE REGISTER FILE Enhanced MCU devices may have banked memory in the GPR area. GPRs are not initialized by a Power-on Reset and are unchanged on all other Resets. Data RAM is available for use as GPR registers by all instructions. The second half of Bank 15 (F60h to FFFh) contains SFRs. All other banks of data memory contain GPRs, starting with Bank 0. MOVFWOFFSET CALLTABLE ORG 0xnn00 TABLEADDWFPCL RETLW0xnn RETLW0xnn RETLW0xnn . . . |
Similar Part No. - PIC18F4431 |
|
Similar Description - PIC18F4431 |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
