Rainbow Electronics ATtiny43U - Manual (Page 20)

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8048B–AVR–03/09
ATtiny43U
5.5 I/O Memory
The I/O space definition of the ATtiny43U is shown in “Register Summary” on page 167 .
All I/Os and peripherals are placed in the I/O space. All I/O locations may be accessed by the
LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32 general purpose
working registers and the I/O space. I/O Registers within the address range 0x00 - 0x1F are
directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single
bits can be checked by using the SBIS and SBIC instructions. See the instruction set section for
more details. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 -
0x3F must be used. When addressing I/O Registers as data space using LD and ST instruc-
tions, 0x20 must be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most
other AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore
be used on registers containing such Status Flags. The CBI and SBI instructions work with reg-
isters 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
5.5.1 General Purpose I/O Registers
ATtiny43U contains three General Purpose I/O Registers. These registers can be used for stor-
ing any information, and they are particularly useful for storing global variables and status flags.
General Purpose I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible
using the SBI, CBI, SBIS, and SBIC instructions.
5.6 Register Description
5.6.1 EEAR – EEPROM Address Register
• Bits 7:6 – Res: Reserved Bit
These bits are reserved and will always read zero.
• Bits 5:0 – EEAR[5:0]: EEPROM Address
The EEPROM Address Register – EEAR – specifies the EEPROM address. The EEPROM data
bytes are addressed linearly in the range 0...(64-1). The initial value of EEAR is undefined. A
proper value must be written before the EEPROM may be accessed.
Bit 7 6 5 4 3 2 1 0
0x1E (0x3E) - - EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEAR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 X X X X X X