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OP296 Folha de dados(PDF) 51 Page - Analog Devices |
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OP296 Folha de dados(HTML) 51 Page - Analog Devices |
51 / 88 page ADuC841/ADuC842/ADuC843 Rev. 0 | Page 51 of 88 DUAL DATA POINTER The ADuC841/ADuC842/ADuC843 incorporate two data pointers. The second data pointer is a shadow data pointer and is selected via the data pointer control SFR (DPCON). DPCON also includes some useful features such as automatic hardware post-increment and post-decrement as well as automatic data pointer toggle. DPCON is described in Table 21. DPCON Data Pointer Control SFR SFR Address A7H Power-On Default 00H Bit Addressable No Table 21. DPCON SFR Bit Designations Bit No. Name Description 7 ---- Reserved. 6 DPT Data Pointer Automatic Toggle Enable. Cleared by the user to disable autoswapping of the DPTR. Set in user software to enable automatic toggling of the DPTR after each each MOVX or MOVC instruction. 5 DP1m1 Shadow Data Pointer Mode. These two bits enable extra modes of the shadow data pointer’s operation, allowing for more compact and more efficient code size and execution. m1 m0 Behavior of the shadow data pointer. 0 0 8052 behavior. 0 1 DPTR is post-incremented after a MOVX or a MOVC instruction. 1 0 DPTR is post-decremented after a MOVX or MOVC instruction. 4 DP1m0 1 1 DPTR LSB is toggled after a MOVX or MOVC instruction. (This instruction can be useful for moving 8-bit blocks to/from 16-bit devices.) 3 DP0m1 Main Data Pointer Mode. These two bits enable extra modes of the main data pointer operation, allowing for more compact and more efficient code size and execution. m1 m0 Behavior of the main data pointer. 0 0 8052 behavior. 0 1 DPTR is post-incremented after a MOVX or a MOVC instruction. 1 0 DPTR is post-decremented after a MOVX or MOVC instruction. 1 1 DPTR LSB is toggled after a MOVX or MOVC instruction. 2 DP0m0 (This instruction can be useful for moving 8-bit blocks to/from 16-bit devices.) 1 ---- This bit is not implemented to allow the INC DPCON instruction toggle the data pointer without incrementing the rest of the SFR. 0 DPSEL Data Pointer Select. Cleared by the user to select the main data pointer. This means that the contents of this 24-bit register are placed into the three SFRs: DPL, DPH, and DPP. Set by the user to select the shadow data pointer. This means that the contents of a separate 24-bit register appears in the three SFRs: DPL, DPH, and DPP. Note 1: This is the only place where the main and shadow data pointers are distinguished. Everywhere else in this data sheet wherever the DPTR is mentioned, operation on the active DPTR is implied. Note 2: Only MOVC/MOVX @DPTR instructions are relevant above. MOVC/MOVX PC/@Ri instructions do not cause the DPTR to automatically post increment/decrement, and so on. To illustrate the operation of DPCON, the following code copies 256 bytes of code memory at address D000H into XRAM starting from Address 0000H. MOV DPTR,#0 ; Main DPTR = 0 MOV DPCON,#55H ; Select shadow DPTR ; DPTR1 increment mode, ; DPTR0 increment mode ; DPTR auto toggling ON MOV DPTR,#0D000H ; Shadow DPTR = D000H MOVELOOP: CLR A MOVC A,@A+DPTR ; Get data ; Post Inc DPTR ; Swap to Main DPTR (Data) MOVX @DPTR,A ; Put ACC in XRAM ; Increment main DPTR ; Swap Shadow DPTR (Code) MOV A, DPL JNZ MOVELOOP |
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