PIC17C7XX_13 Datasheet, PDF (62/306 Pages) Microchip Technology – High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
8.2 Table Writes to External Memory
Table writes to external memory are always two-cycle
instructions. The second cycle writes the data to the
external memory location. The sequence of events for
an external memory write are the same for an internal
write.
8.2.1 TABLE WRITE CODE
The “i” operand of the TABLWT instruction can specify
that the value in the 16-bit TBLPTR register is automat-
ically incremented (for the next write). In Example 8-1,
the TBLPTR register is not automatically incremented.
EXAMPLE 8-1: TABLE WRITE
CLRWDT
MOVLW
MOVWF
MOVLW
MOVWF
MOVLW
TLWT
MOVLW
TABLWT
; Clear WDT
HIGH (TBL_ADDR) ; Load the Table
TBLPTRH
; address
LOW (TBL_ADDR) ;
TBLPTRL
;
HIGH (DATA)
; Load HI byte
1, WREG
; in TABLATH
LOW (DATA)
; Load LO byte
0,0,WREG
; in TABLATL
; and write to
; program memory
; (Ext. SRAM)
FIGURE 8-5:
TABLWT WRITE TIMING (EXTERNAL MEMORY)
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
AD15:AD0
PC
PC+1
TBL
Data out PC+2
Instruction
Fetched
Instruction
Executed
TABLWT
INST (PC+1)
INST (PC-1)
TABLWT cycle1 TABLWT cycle2
Data write cycle
ALE
OE
'1'
WR
INST (PC+2)
INST (PC+1)
Note: If external write and GLINTD = '1' and Enable bit = '1', then when '1'  Flag bit, do table write.
The highest pending interrupt is cleared.
DS30289C-page 62
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