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PIC16F84A Datasheet(PDF) 19 Page - Microchip Technology |
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PIC16F84A Datasheet(HTML) 19 Page - Microchip Technology |
19 / 124 page ![]() PIC16F8X © 1998 Microchip Technology Inc. DS30430C-page 19 4.5 Indirect Addressing; INDF and FSR Registers The INDF register is not a physical register. Address- ing INDF actually addresses the register whose address is contained in the FSR register (FSR is a pointer). This is indirect addressing. EXAMPLE 4-1: INDIRECT ADDRESSING • Register file 05 contains the value 10h • Register file 06 contains the value 0Ah • Load the value 05 into the FSR register • A read of the INDF register will return the value of 10h • Increment the value of the FSR register by one (FSR = 06) • A read of the INDF register now will return the value of 0Ah. Reading INDF itself indirectly (FSR = 0) will produce 00h. Writing to the INDF register indirectly results in a no-operation (although STATUS bits may be affected). A simple program to clear RAM locations 20h-2Fh using indirect addressing is shown in Example 4-2. EXAMPLE 4-2: HOW TO CLEAR RAM USING INDIRECT ADDRESSING movlw 0x20 ;initialize pointer movwf FSR ; to RAM NEXT clrf INDF ;clear INDF register incf FSR ;inc pointer btfss FSR,4 ;all done? goto NEXT ;NO, clear next CONTINUE : ;YES, continue An effective 9-bit address is obtained by concatenating the 8-bit FSR register and the IRP bit (STATUS<7>), as shown in Figure 4-1. However, IRP is not used in the PIC16F8X. FIGURE 4-1: DIRECT/INDIRECT ADDRESSING Direct Addressing RP1 RP0 6 from opcode 0 IRP 7 (FSR) 0 Indirect Addressing bank select location select bank select location select 00 01 10 11 00h 7Fh 00h 0Bh 0Ch 2Fh (1) 30h (1) 7Fh not used Bank 0 Bank 1 Bank 2 Bank 3 Note 1: PIC16F83 and PIC16CR83 devices. 2: PIC16F84 and PIC16CR84 devices 3: For memory map detail see Figure 4-1. 4Fh (2) 50h (2) Addresses map back to Bank 0 Data Memory (3) not used |
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