ATTINY12 ATMEL Corporation, ATTINY12 Datasheet - Page 29

• Manufacturer Part Number: ATTINY12
• Description: 8-bit AVR Microcontroller with 1K Byte Flash
• Manufacturer: ATMEL Corporation

MCU Control Register –
MCUCR
1006D–AVR–07/03
The MCU Control Register contains control bits for general MCU functions.
Note:
• Bit 7 - Res: Reserved Bit
This bit is a reserved bit in the ATtiny11/12 and always reads as zero.
• Bit 6 - Res: Reserved Bit in ATtiny11
This bit is a reserved bit in the ATtiny11 and always reads as zero.
• Bit 6 - PUD: Pull-up Disable in ATtiny12
Setting this bit, disables all pull-ups on port B. If this bit is cleared, the pull-ups can be
individually enabled as described in section “I/O Port B” on page 43.
• Bit 5 - SE: Sleep Enable
The SE bit must be set (one) to make the MCU enter the Sleep Mode when the SLEEP
instruction is executed. To avoid the MCU entering the Sleep Mode unless it is the pro-
grammer’s purpose, it is recommended to set the Sleep Enable SE bit just before the
execution of the SLEEP instruction.
• Bit 4 - SM: Sleep Mode
This bit selects between the two available sleep modes. When SM is cleared (zero), Idle
Mode is selected as Sleep Mode. When SM is set (one), Power-down Mode is selected
as Sleep Mode. For details, refer to the paragraph “Sleep Modes” below.
• Bits 3, 2 - Res: Reserved Bits
These bits are reserved bits in the ATtiny11/12 and always read as zero.
• Bits 1, 0 - ISC01, ISC00: Interrupt Sense Control0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the
corresponding interrupt mask are set. The following table shows how to set the ISC bits
to generate an external interrupt:
Table 13. Interrupt 0 Sense Control
The value on the INT0 pin is sampled before detecting edges. If edge interrupt is
selected, pulses that last longer than one CPU clock period will generate an interrupt.
Shorter pulses are not guaranteed to generate an interrupt. If low-level interrupt is
selected, the low level must be held until the completion of the currently executing
Bit
$35
Read/Write
Initial Value
ISC01
0
0
1
1
The Pull-up Disable (PUD) bit is only available in ATtiny12.
ISC00
0
1
0
1
R
7
0
-
(PUD)
Description
The low level of INT0 generates an interrupt request.
Any change on INT0 generates an interrupt request
The falling edge of INT0 generates an interrupt request.
The rising edge of INT0 generates an interrupt request.
R(/W)
6
0
R/W
SE
5
0
R/W
SM
4
0
R
3
0
-
R
2
0
-
ISC01
R/W
ATtiny11/12
1
0
ISC00
R/W
0
0
MCUCR
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