AT89LS51 Atmel Corporation, AT89LS51 Datasheet - Page 9

• Manufacturer Part Number: AT89LS51
• Manufacturer: Atmel Corporation

Specifications of AT89LS51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 16 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Uart: 1
• Sram (kbytes): 0.125
• Operating Voltage (vcc): 2.7 to 4.0
• Timers: 2
• Isp: SPI
• Watchdog: Yes

6. Memory Organization
6.1
6.2
7. Watchdog Timer (One-time Enabled with Reset-out)
3053C–MICRO–6/08
Program Memory
Data Memory
Table 5-3.
MCS-51 devices have a separate address space for Program and Data Memory. Up to 64K
bytes each of external Program and Data Memory can be addressed.
If the EA pin is connected to GND, all program fetches are directed to external memory.
On the AT89LS51, if EA is connected to V
FFFH are directed to internal memory and fetches to addresses 1000H through FFFFH are
directed to external memory.
The AT89LS51 implements 128 bytes of on-chip RAM. The 128 bytes are accessible via direct
and indirect addressing modes. Stack operations are examples of indirect addressing, so the
128 bytes of data RAM are available as stack space.
The WDT is intended as a recovery method in situations where the CPU may be subjected to
software upsets. The WDT consists of a 14-bit counter and the Watchdog Timer Reset
(WDTRST) SFR. The WDT is defaulted to disable from exiting reset. To enable the WDT, a user
must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H). When
the WDT is enabled, it will increment every machine cycle while the oscillator is running. The
WDT timeout period is dependent on the external clock frequency. There is no way to disable
the WDT except through reset (either hardware reset or WDT overflow reset). When WDT over-
flows, it will drive an output RESET HIGH pulse at the RST pin.
AUXR1
Addressable
–
DPS
Address = A2H
Not Bit
Bit
Data Pointer Register Select
Reserved for future expansion
DPS
0
1
–
7
AUXR1: Auxiliary Register 1
Selects DPTR Registers DP0L, DP0H
Selects DPTR Registers DP1L, DP1H
–
6
–
5
–
4
CC
, program fetches to addresses 0000H through
–
3
–
2
Reset Value = XXXXXXX0B
–
1
AT89LS51
DPS
0
9