Datasheet
Table Of Contents
- Features
- Description
- Block Diagram
- SFR Mapping
- Pin Configurations
- Oscillators
- Enhanced Features
- Dual Data Pointer Register DPTR
- Expanded RAM (XRAM)
- Reset
- Power Monitor
- Timer 2
- Programmable Counter Array PCA
- Serial I/O Port
- Interrupt System
- Power Management
- Keyboard Interface
- 2-wire Interface (TWI)
- Serial Port Interface (SPI)
- Hardware Watchdog Timer
- ONCE(TM) Mode (ON Chip Emulation)
- Power-off Flag
- EEPROM Data Memory
- Reduced EMI Mode
- Flash Memory
- Electrical Characteristics
- Absolute Maximum Ratings
- DC Parameters
- AC Parameters
- Explanation of the AC Symbols
- External Program Memory Characteristics
- External Program Memory Read Cycle
- External Data Memory Characteristics
- External Data Memory Write Cycle
- External Data Memory Read Cycle
- Serial Port Timing - Shift Register Mode
- Shift Register Timing Waveforms
- External Clock Drive Waveforms
- AC Testing Input/Output Waveforms
- Float Waveforms
- Clock Waveforms
- Ordering Information
- Packaging Information
- Table of Contents
18
AT89C51ID2
4289C–8051–11/05
Idle Modes • IDLE modes are achieved by using any instruction that writes into PCON.0 bit (IDL)
• IDLE modes A and B depend on previous software sequence, prior to writing into
PCON.0 bit:
• IDLE MODE A: OscA is running (OscAEn = 1) and selected (CKS = 1)
• IDLE MODE B: OscB is running (OscBEn = 1) and selected (CKS = 0)
• The unused oscillator OscA or OscB can be stopped by software by clearing
OscAEn or OscBEn respectively.
• IDLE mode can be canceled either by Reset, or by activation of any enabled
interruption
• In both cases, PCON.0 bit (IDL) is cleared by hardware
• Exit from IDLE modes will leave Oscillators control bits (OscEnA, OscEnB, CKS)
unchanged.
Power Down Modes • POWER DOWN modes are achieved by using any instruction that writes into
PCON.1 bit (PD)
• POWER DOWN modes A and B depend on previous software sequence, prior to
writing into PCON.1 bit:
• Both OscA and OscB will be stopped.
• POWER DOWN mode can be cancelled either by a hardware Reset, an external
interruption, or the keyboard interrupt.
• By Reset signal: The CPU will restart according to OSC bit in Hardware Security Bit
(HSB) register.
• By INT0 or INT1 interruption, if enabled: (standard behavioral), request on Pads
must be driven low enough to ensure correct restart of the oscillator which was
selected when entering in Power down.
• By keyboard Interrupt if enabled: a hardware clear of the PCON.1 flag ensure the
restart of the oscillator which was selected when entering in Power down.
Table 20. Overview
PCON.1 PCON.0 OscBEn OscAEn CKS Selected Mode Comment
00 0 11
NORMAL MODE
A, OscB stopped
Default mode after power-up or
Warm Reset
00 1 11
NORMAL MODE
A, OscB running
Default mode after power-up or
Warm Reset + OscB running
00 1 00
NORMAL MODE
B, OscA stopped
OscB running and selected
00 1 10
NORMAL MODE
B, OscA running
OscB running and selected +
OscA running
XX 0 0XINVALID
OscA & OscB cannot be stopped
at the same time
XX X 01INVALID
OscA must not be stopped, as
used for CPU and peripherals
XX 0 X0INVALID
OscB must not be stopped as
used for CPU and peripherals
0 1 X 1 1 IDLE MODE A
The CPU is off, OscA supplies the
peripherals, OscB can be disabled
(OscBEn = 0)