![](http://datasheet.mmic.net.cn/230000/7721_datasheet_15568108/7721_9.png)
7721 Group User’s Manual
ii
Table of contents
CHAPTER 4 RESET
4.1 Hardware reset ...................................................................................................................... 4-2
4.1.1 Pin state.......................................................................................................................... 4-3
4.1.2 State of CPU, SFR area, and internal RAM area..................................................... 4-4
4.1.3 Internal processing sequence after reset ................................................................. 4-11
4.1.4 Time supplying “L” level to RESET pin.................................................................... 4-12
4.2 Software reset...................................................................................................................... 4-13
CHAPTER 5 CLOCK GENERATING CIRCUIT
5.1 Oscillation circuit examples ............................................................................................... 5-2
5.1.1 Connection example using resonator/oscillator.......................................................... 5-2
5.1.2 Externally generated clock input example.................................................................. 5-2
5.2 Clocks.......................................................................................................................................5-3
5.2.1 Clocks generated in clock generating circuit ............................................................. 5-4
5.3 Stop mode .............................................................................................................................. 5-5
5.3.1 Stop mode ...................................................................................................................... 5-5
[Precautions for Stop mode] .................................................................................................. 5-8
5.4 Wait mode............................................................................................................................... 5-9
5.4.1 Wait mode ...................................................................................................................... 5-9
[Precautions for Wait mode]................................................................................................. 5-11
CHAPTER 6 INPUT/OUTPUT PINS
6.1 Overview ..................................................................................................................................6-2
6.2 Programmable I/O ports ...................................................................................................... 6-2
6.2.1 Direction register............................................................................................................ 6-3
6.2.2 Port register.................................................................................................................... 6-4
6.3 Examples of handling unused pins .................................................................................. 6-7
CHAPTER 7 INTERRUPTS
7.1 Overview ..................................................................................................................................7-2
7.2 Interrupt sources................................................................................................................... 7-4
7.3 Interrupt control .................................................................................................................... 7-5
7.3.1 Interrupt disable flag (I) ................................................................................................ 7-7
7.3.2 Interrupt request bit....................................................................................................... 7-7
7.3.3 Interrupt priority level select bits and processor interrupt priority level (IPL) .......7-7
7.4 Interrupt priority level.......................................................................................................... 7-9
7.5 Interrupt priority level detection circuit ........................................................................ 7-10
7.6 Interrupt priority level detection time ............................................................................ 7-12
7.7 Sequence from acceptance of interrupt request until execution of interrupt
routine.................................................................................................................................... 7-13
7.7.1 Change in IPL at acceptance of interrupt request..................................................7-14
7.7.2 Push operation for registers....................................................................................... 7-15
7.8 Return from interrupt routine........................................................................................... 7-16
7.9 Multiple interrupts............................................................................................................... 7-16
7.10 External interrupts (INTi interrupt) ............................................................................... 7-18
7.10.1 Functions of INTi interrupt request bit.................................................................... 7-20
7.10.2 Switching of INTi interrupt request occurrence factor ..........................................7-21
7.11 Precautions for interrupts............................................................................................... 7-22