SM8951B Datasheet, PDF (17/18 Pages) SyncMOS Technologies,Inc – 8-Bits Micro-controller

SyncMOS Technologies International, Inc.
SM8951B
8-Bits Micro-controller
With4KBFlashROM&128bytesRAM embedded
Idle Mode:
The user can put the device into idle mode by writing 1 to the bit PCON.0. The instruction that sets the idle bit is the
last instruction that will be executed before the device goes into Idle Mode. In the Idle Mode, the clock to the CPU is
halted, but not to the Interrupt, Timer and Serial port blocks. This forces the CPU state to be frozen; the Program
counter, the Stack Pointer, the Program Status Word, the Accumulator and the other registers hold their contents. The
ALE and PSEN pins are held high during the idle state. The port pins hold the logical states they had at the time idle
was activated. The idle mode can be terminated in two ways. Since the interrupt controller is still active, the activation
of any enabled interrupt can wake up the processor. This will automatically clear the idle bit, terminate the idle mode,
and the Interrupt Service Routine (ISR) will be executed. After the ISR, execution of the program will continue from
the instruction that put the device into idle mode.
The Idle mode can also be exited by activating the reset. The device can be put into reset either applying a high on the
external RST pin or a Power on reset condition. The external reset pin has to be held high for at least two machine
cycles to be recognized as a valid reset. In the reset condition the program counter is reset to 0000H and all the SFRs
are set to the reset condition. Since the clock is already running there is no delay and execution start immediately.
When the SM8951B is exiting from an idle mode with a reset, the instruction following the one that put the device
into idle mode is not executed. So there is no danger of unexpected writes.
Power Down Mode:
The device can be put into Power Down mode by writing 1 to bit PCON.1. The instruction that does this will be the
last instruction to be executed before the device goes into Power Down mode. In the Power Down mode, all the
clocks are stopped and the device comes to a halt. All activity is completely stopped and the power consumption is
reduced to the lowest possible value. In this state the ALE and PSEN pins are pull low. The port pins output the
values held by their respective SFRs.
The status of external pins during Idle and Power Down:
Mode
Idle
Idle
Power Down
Power Down
Program
Memory
Internal
External
Internal
External
ALE /PSEN PORT0 PORT1
1
1
Data
Data
1
1
Float
Data
0
0
Data
Data
0
0
Float
Data
PORT2
Data
Address
Data
Data
PORT3
Data
Data
Data
Data
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M022Ver:BSM8951B
17
06/2009