at43usb355 ATMEL Corporation, at43usb355 Datasheet - Page 9

• Manufacturer Part Number: at43usb355
• Description: At43usb355 Full-speed Usb Microcontroller With Embedded Hub, Adc And Pwm
• Manufacturer: ATMEL Corporation

X-, Y- and Z-
Registers
ALU – Arithmetic
Logic Unit
Program Memory
2603G–USB–04/06
All register operating instructions in the instruction set have direct and single cycle access to
all registers. The only exception is the five constant arithmetic and logic instructions SBCI,
SUBI, CPI, ANDI, and ORI between a constant and a register, and the LDI instruction for load
immediate constant data. These instructions apply to the second half of the registers in the
register file – R16..R31. The general SBC, SUB, CP, AND, and OR and all other operations
between two registers or on a single register apply to the entire register file.
As shown in Table 1, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically imple-
mented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y-, and Z-registers can be set to index any register in the file.
Registers R26..R31 contain some added functions to their general-purpose usage. These reg-
isters are address pointers for indirect addressing of the Data Space. The three indirect
address registers X, Y, and Z are defined as:
In the different addressing modes these address registers have functions as fixed displace-
ment, automatic increment and decrement (see the descriptions for the different instructions).
The high-performance AVR ALU operates in direct connection with all 32 general-purpose
working registers. Within a single clock cycle, ALU operations between registers in the register
file are executed. The ALU operations are divided into three main categories – arithmetic, log-
ical and bit-functions.
The AT43USB355E contains 24K bytes on-chip downloadable memory for program storage
while the AT43USB355M has a masked programmable ROM. Since all instructions are 16- or
32-bit words, the program memory is organized as 12K x 16. The AT43USB355 Program
Counter (PC) is 14 bits wide, thus addressing the 12,288 program memory addresses.
Constant tables can be allocated within the entire program memory address space (see the
LPM - Load Program Memory instruction description).
X-register
Z-register
Y-register
15
7
15
7
15
7
R29 ($1D)
R27 ($1B)
R30 ($1F)
YH
XH
ZH
0
0
0
7
7
7
AT43USB355
R28 ($1C)
R26 ($1A)
R31 ($1E)
XL
YL
ZL
0
0
0
0
0
0
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