AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 12

• 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

3.1.1
12
AT89LP51/52
External Program Memory Interface
Figure 3-1.
The AT89LP51/52 uses the standard 8051 external program memory interface with the upper
address on Port 2, the lower address and data in/out multiplexed on Port 0, and the ALE and
PSEN strobes. Program memory addresses are always 16-bits wide, even though the actual
amount of program memory used may be less than 64K byes. External program execution sacri-
fices two full 8-bit ports, P0 and P2, to the function of addressing the program memory.
Figure 3-2
a 16-bit linear address. Port 0 serves as a multiplexed address/data bus to the ROM. The
Address Latch Enable strobe (ALE) is used to latch the lower address byte into an external reg-
ister so that Port 0 can be freed for data input/output. Port 2 provides the upper address byte
throughout the operation. PSEN strobes the external memory.
Figure 3-3
stant rate of 1/3 of the system clock with a 1/3 duty cycle. PSEN is emitted at a similar rate, but
with 50% duty cycle. The new address changes in the middle of the ALE pulse for latching on
the falling edge and is tristated at the falling edge of PSEN. The instruction data is sampled from
P0 and latched internally during the high phase of the clock prior to the rising edge of PSEN.
This timing applies to both Compatibility and Fast modes. In Compatibility mode there is no dif-
ference in instruction timing between internal and external execution.
Figure 3-2.
shows a hardware configuration for accessing up to 64K bytes of external ROM using
shows the timing of the external program memory interface. ALE is emitted at a con-
0100
0000
1000
0000
01FF
007F
0FFF
FFFF
Program Memory Map
Executing from External Program Memory
Atmel Signature Array
User Signature Array
External Program
Internal Program
(XCODE: 60KB)
(CODE: 4KB)
AT89LP51
Memory
Memory
P1
P3
AT89LP
PSEN
ALE
P0
P2
01FF
0100
007F
0000
2000
0000
FFFF
1FFF
LATCH
Atmel Signature Array
User Signature Array
External Program
Internal Program
(XCODE: 56KB)
(CODE: 8KB)
AT89LP52
Memory
Memory
EXTERNAL
PROGRAM
INSTR.
OE
MEMORY
ADDR
SIGEN=1
SIGEN=0
3709D–MICRO–12/11