Datasheet

12.7.5. MCUCR – MCU Control Register
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 instructions, 0x20 must be added to these offset
addresses. The device is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space
from 0x60 in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
Name: MCUCR
Offset: 0x35
Reset: 0x00
Property: When addressing I/O Registers as data space the offset address is 0x55
Bit 7 6 5 4 3 2 1 0
SRE SRW10
Access
R/W R/W
Reset 0 0
Bit 7 – SRE: External SRAM/XMEM Enable
Writing SRE to one enables the External Memory Interface. The pin functions AD7:0, A15:8, ALE, WR,
and RD are activated as the alternate pin functions. The SRE bit overrides any pin direction settings in
the respective data direction registers. Writing SRE to zero, disables the External Memory Interface and
the normal pin and data direction settings are used.
Bit 6 – SRW10: Wait-state Select Bit
For a detailed description in non-ATmega103 compatibility mode, see common description for the SRWn
bits below (XMCRA description). In ATmega103 compatibility mode, writing SRW10 to one enables the
wait-state and one extra cycle is added during read/write strobe as shown in Figure 12-7 External Data
Memory Cycles with SRWn1 = 0 and SRWn0 = 1(1) on page 38.
Atmel ATmega64A [DATASHEET]
Atmel-8160E-ATmega64A_Datasheet_Complete-09/2015
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