AT89C51RE2 Atmel Corporation, AT89C51RE2 Datasheet - Page 25

• Manufacturer Part Number: AT89C51RE2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RE2

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Spi: 1
• Uart: 2
• Sram (kbytes): 8.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART/OCD
• Watchdog: Yes

Extended Stack
7663E–8051–10/08
FFFFh
0000h
Logical MCU
Address
Standard C51 Stack mode EES = 0
FFh
00h
256 bytes
IRAM
XRAM
SP Value
FFh
00h
The lowest bytes of the XRAM may be used to allow extension of the stack pointer.
The extended stack allows to extend the standard C51 stack over the 256 bytes of internal RAM.
When the extended stack mode is activated (EES bit in AUXR1), the stack pointer (SP) can
grow in the lower 256 bytes of the XRAM area.
The stack extension consists in a 9 bits stack pointer where the ninth bit is located in SP9 (bit 6
of AUXR1). The SP9 then indicates if the stack pointer belongs to the internal RAM (SP9
cleared) or to the XRAM memory (SP9 set).
To ensure backward compatibility with standard C51 architecture, the extended mode is disable
at chip reset.
Figure 7. Stack modes
Figure 8. AUXR1 register
AUXR1- Auxiliary Register 1(0A2h)
Number
256 SP values
rollover within 256B of IRAM
EES
Bit
7
7
Mnemonic
SP9
EES
Bit
6
Description
Enable Extended Stack
Set to enable the extended stack
Clear to disable the extended stack (default value)
U2
5
This bit allows the selection of the stack extended mode.
FFFFh
00FFh
0000h
Logical MCU
Address
FFh
00h
Extended Stack mode Stack EES = 1
4
-
256 bytes
IRAM
XRAM
GF2
3
SP Value
FFh
FFh
00h
00h
SP9=1
SP9=0
2
0
AT89C51RE2
512 SP Values
rollover in:
256B of IRAM
+
lower 256B of XRAM
1
-
DPS
0
25