PIC18 cheatsheet
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BCFBSFBTFSCBTFSSBTG
BCBNBNCBNNBNOVBNZBOVBRABZCALLCLRWDTDAWGOTONOPPOPPUSHRCALLRESETRETFIERETLWRETURNSLEEP
ADDLWANDLWIORLWLFSRMOVLBMOVLWMULLWRETLWSUBLWXORLW
TBLRD*TBLRD*+TBLRD*-TBLRD+*TBLWT*TBLWT*+TBLWT*-TBLWT+*

TBLRD*+

Detailed reference for the TBLRD*+ instruction in PIC18 ISA.

Description

The TBLRD+ instruction reads an 8‑bit byte from program memory at the address currently held in the Table Pointer registers (TBLPAG, TBLPTRU, TBLPTRH, TBLPTRL). The value read is moved into WREG.

After the data is transferred, the Table Pointer is post‑incremented, so the next execution of TBLRD+ will read the next byte in program memory.

  • The instruction has no destination (d) or access‑bank (a) operands; it operates on the current table pointer value.
  • It is used in conjunction with the TBLPTR registers, which must be loaded beforehand.
  • A variant, TBLRD-, performs a post‑decrement.

Examples

; Assume TBLPAG = 0x00: read first byte of a table
TBLRD+ ; W = program memory[0x00], TBLPAG becomes 0x01
; Assume TBLPAG = 0x1F: read a mid‑range table entry
TBLRD+ ; W = program memory[0x1F], TBLPAG becomes 0x20
; Assume TBLPAG = 0xFF: read the last byte of the current bank
TBLRD+ ; W = program memory[0xFF], TBLPAG becomes 0x100 (wraps to next bank if applicable)
; After reading at 0x00 with TBLRD+, TBLPAG is 0x01: read the next entry
TBLRD+ ; W = program memory[0x01], TBLPAG becomes 0x02
; Assume TBLPAG = 0x80: read a byte near the middle of program memory
TBLRD+ ; W = program memory[0x80], TBLPAG becomes 0x81