AT89LP828 Atmel Corporation, AT89LP828 Datasheet - Page 17

• Manufacturer Part Number: AT89LP828
• Manufacturer: Atmel Corporation

Specifications of AT89LP828

• Flash (kbytes): 8 Kbytes
• Max. Operating Frequency: 25 MHz
• Cpu: 8051-1C
• Max I/o Pins: 30
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.75
• Eeprom (bytes): 1024
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

5.1
3654A–MICRO–8/09
Enhanced Dual Data Pointers
Figure 5-3.
The AT89LP428/828 provides two 16-bit data pointers: DPTR0 formed by the register pair
DPOL and DPOH (82H an 83H), and DPTR1 formed by the register pair DP1L and DP1H (84H
and 85H). The data pointers are used by several instructions to access the program or data
memories. The Data Pointer Configuration Register (DPCF) controls operation of the dual data
pointers
instructions including the DPTR operand. Each data pointer may be accessed at its respective
SFR addresses regardless of the DPS value. The AT89LP428/828 provides two methods for
fast context switching of the data pointers:
• Bit 2 of DPCF is hard-wired as a logic 0. The DPS bit may be toggled (to switch data pointers)
• In some cases, both data pointers must be used simultaneously. To prevent frequent toggling
simply by incrementing the DPCF register, without altering other bits in the register
unintentionally. This is the preferred method when only a single data pointer will be used at
one time.
of DPS, the AT89LP428/828 supports a prefix notation for selecting the opposite data pointer
per instruction. All DPTR instructions, with the exception of JMP @A+DPTR, when prefixed
with an 0A5H opcode will use the inverse value of DPS (DPS) to select the data pointer.
Some assemblers may support this operation by using the /DPTR operand. For example,
the following code performs a block copy within EDATA:
EX:
COPY: MOVX A, @DPTR
Fetch Immediate Operand
ALU Operation Execute
(Table
Fetch Next Instruction
Total Execution Time
INC
MOV
MOV
MOV
MOV
INC
MOVX @/DPTR, A
INC
DJNZ R7, COPY
Result Write Back
Two-cycle ALU Operation (Example: ADD A, #data)
5-4). The DPS bit in DPCF selects which data pointer is currently referenced by
System Clock
DPCF
DPCF, #00H
DPTR, #SRC
/DPTR, #DST
R7, #BLKSIZE
DPTR
/DPTR
; Toggle DPS
; DPS = 0
; load source address to dptr0
; load destination address to dptr1
; number of bytes to copy
; read source (dptr0)
; next src (dptr0+1)
; write destination (dptr1)
; next dst (dptr1+1)
T
1
T
2
AT89LP428/828
T
3
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