参数资料
型号: AT80C51RD2-SLSUM
厂商: Atmel
文件页数: 6/81页
文件大小: 0K
描述: IC 8051 MCU 5V SPI 20MHZ 44-PLCC
标准包装: 972
系列: 80C
核心处理器: 8051
芯体尺寸: 8-位
速度: 40MHz
连通性: UART/USART
外围设备: POR,PWM,WDT
输入/输出数: 32
程序存储器类型: ROMless
RAM 容量: 1K x 8
电压 - 电源 (Vcc/Vdd): 4.5 V ~ 5.5 V
振荡器型: 内部
工作温度: -40°C ~ 85°C
封装/外壳: 44-PLCC
包装: 管件
14
4113D–8051–01/09
AT80C51RD2
8.
Expanded RAM (XRAM)
The AT80C51RD2 devices provide additional Bytes of Random Access Memory (RAM) space
for increased data parameter handling and high level language usage.
The devices have expanded RAM in external data space; maximum size and location are
described in Table 8-1.
Table 8-1.
Expanded RAM
The AT80C51RD2 has internal data memory that is mapped into four separate segments.
The four segments are:
1.
The Lower 128 bytes of RAM (addresses 00h to 7Fh) are directly and indirectly
addressable.
2.
The Upper 128 bytes of RAM (addresses 80h to FFh) are indirectly addressable only.
3.
The Special Function Registers (SFRs) (addresses 80h to FFh) are directly address-
able only.
4.
The expanded RAM bytes are indirectly accessed by MOVX instructions, and with the
EXTRAM bit cleared in the AUXR register (see Table 8-1).
The lower 128 bytes can be accessed by either direct or indirect addressing. The Upper 128
bytes can be accessed by indirect addressing only. The Upper 128 bytes occupy the same
address space as the SFR. That means they have the same address, but are physically sepa-
rate from SFR space.
Figure 8-1.
Internal and External Data Memory Address
When an instruction accesses an internal location above address 7Fh, the CPU knows whether
the access is to the upper 128 bytes of data RAM or to SFR space by the addressing mode used
in the instruction.
Instructions that use direct addressing access SFR space. For example: MOV 0A0H, # data,
accesses the SFR at location 0A0h (which is P2).
XRAM size
Address
Start
End
T83C51RB2/RC2
T80C51RD2
1024
00h
3FFh
XRAM
Upper
128 Bytes
Internal
RAM
Lower
128 Bytes
Internal
RAM
Special
Function
Register
80h
00
0FFh or 3FFh
0FFh
00
0FFh
External
Data
Memory
0000
00FFh up to 03FFh
0FFFFh
indirect accesses
Direct Accesses
Direct or Indirect
Accesses
7Fh
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