AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 14

• Manufacturer Part Number: AT89LP51
• Manufacturer: Atmel Corporation

Specifications of AT89LP51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 36
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 256
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

3.2
3.2.1
3.2.2
3.2.3
3.3
14
Internal Data Memory
External Data Memory
AT89LP51/52
DATA
IDATA
SFR
access the code memory. The User Signature Array may also be modified by the In-Application
Programming interface. When IAP = 1 and SIGEN = 1, MOVX @DPTR instructions will access
the array (See
The AT89LP51/52 contains 256 bytes of general SRAM data memory plus 128 bytes of I/O
memory mapped into a single 8-bit address space. Access to the internal data memory does not
require any configuration. The internal data memory has three address spaces: DATA, IDATA
and SFR; as shown in
internally. See
Figure 3-5.
The first 128 bytes of RAM are directly addressable by an 8-bit address (00H–7FH) included in
the instruction. The lowest 32 bytes of DATA memory are grouped into 4 banks of 8 registers
each. The RS0 and RS1 bits (PSW.3 and PSW.4) select which register bank is in use. Instruc-
tions using register addressing will only access the currently specified bank. The lower 128 bit
addresses are also mapped into DATA addresses 20H—2FH.
The full 256 byte internal RAM can be indirectly addressed using the 8-bit pointers R0 and R1.
The first 128 bytes of IDATA include the DATA space. The hardware stack is also located in the
IDATA space.
The upper 128 direct addresses (80H–FFH) access the I/O registers. I/O registers on AT89LP
devices are referred to as Special Function Registers. The SFRs can only be accessed through
direct addressing. All SFR locations are not implemented. See
SFRs.
AT89LP microcontrollers support a 16-bit external memory address space for up to 64K bytes of
external data memory (XDATA). The external memory space is accessed with the MOVX
instructions. Some internal data memory resources are mapped into portions of the external
LOWER
UPPER
128
128
Internal Data Memory Map
Section 3.4 on page
“External Data Memory”
FFH
7FH
80H
0
Figure
AND INDIRECT
ADDRESSING
ADDRESSING
ACCESSIBLE
BY INDIRECT
ACCESSIBLE
DATA/IDATA
BY DIRECT
IDATA
ONLY
3-5. Some portions of external data memory are also implemented
23).
below for more information.
ADDRESSING
ACCESSIBLE
BY DIRECT
SFR
SPECIAL
FUNCTION
REGISTERS
FFH
80H
Section 4.
PORTS
STATUS AND
CONTROL BITS
REGISTERS
STACK POINTER
ACCUMULATOR
(ETC.)
TIMERS
for a listed of available
3709D–MICRO–12/11