SAM7X256 Atmel Corporation, SAM7X256 Datasheet - Page 50

• Manufacturer Part Number: SAM7X256
• Manufacturer: Atmel Corporation

Specifications of SAM7X256

• Flash (kbytes): 256 Kbytes
• Pin Count: 100
• Max. Operating Frequency: 55 MHz
• Cpu: ARM7TDMI
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 62
• Ext Interrupts: 62
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 2
• Twi (i2c): 1
• Uart: 3
• Can: 1
• Ssc: 1
• Ethernet: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 384
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 64
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 3.3
• Operating Voltage (vcc): 3.0 to 3.6
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 3
• Input Capture Channels: 3
• Pwm Channels: 4
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: No

Programmer’s Model
2.3
2.3.1
2-4
31
Memory formats
Little-endian
Byte at address A+3
Halfword at address A+2
The ARM7TDMI processor views memory as a linear collection of bytes numbered in
ascending order from zero. For example:
•
•
The ARM7TDMI processor is bi-endian and can treat words in memory as being stored
in either:
•
•
Little-endian is traditionally the default format for ARM processors.
The endian format of a CPU dictates where the most significant byte or digits must be
placed in a word. Because numbers are calculated by the CPU starting with the least
significant digits, little-endian numbers are already set up for the processing order.
Endian configuration has no relevance unless data is stored as words and then accessed
in smaller sized quantities (halfwords or bytes).
In little-endian format, the lowest addressed byte in a word is considered the
least-significant byte of the word and the highest addressed byte is the most significant.
So the byte at address 0 of the memory system connects to data lines 7 through 0.
For a word-aligned address A, Figure 2-1 shows how the word at address A, the
halfword at addresses A and A+2, and the bytes at addresses A, A+1, A+2, and A+3
map on to each other when the core is configured as little-endian.
24 23
bytes zero to three hold the first stored word
bytes four to seven hold the second stored word.
Little-endian on page 2-4.
Big-Endian on page 2-5
Note
Byte at address A+2
Figure 2-1 LIttle-endian addresses of bytes and halfwords within words
Copyright © 1994-2001. All rights reserved.
Word at address A
16 15
Byte at address A+1
Halfword at address A
8 7
Byte at address A
ARM DDI 0029G
0