1997 Dec 15
42
Philips Semiconductors
Product specification
8-bit microcontrollers
P83C524; P80C528; P83C528
15.2
Idle Mode
The instruction that sets PCON.0 is the last instruction
executed in the normal operating mode before Idle mode
is activated. Once in the Idle mode, the CPU status is
preserved in its entirety: the Stack Pointer, Program
Counter, Program Status Word, Accumulator, RAM and all
other registers maintain their data during Idle mode. The
status of external pins during Idle mode is shown in
Table 28.
There are three ways to terminate the Idle mode:
Activation of any enabled interrupt will cause PCON.0 to
be cleared by hardware terminating Idle mode. The
interrupt is serviced, and following return from interrupt
instruction RETI, the next instruction to be executed will
be the one which follows the instruction that wrote a
logic 1 to PCON.0.
The flag bits GF0 and GF1 may be used to determine
whether the interrupt was received during normal
execution or during the Idle mode. For example, the
instruction that writes to PCON.0 can also set or clear
one or both flag bits. When Idle mode is terminated by
an interrupt, the service routine can examine the status
of the flag bits.
The second way of terminating the Idle mode is with an
external hardware reset. Since the oscillator is still
running, the hardware reset is required to be active for
two machine cycles (24 oscillator periods) to complete
the reset operation.
The third way of terminating the Idle mode is by internal
watchdog reset.
15.3
Power-down Mode
The instruction that sets PCON.1 is the last executed prior
to going into the Power-down mode. The oscillator is
stopped. Note that the Power-down mode also can be
entered when the watchdog has been enabled. The
Power-down mode can be terminated by an external
RESET in the same way as in the 80C51 or in addition by
any one of the two external interrupts, IE0 or IE1 (see
Section 15.4). A reset generated by the WDT terminates
the Power-down mode in the same way as an external
RESET.
The status of the external pins during Power-down mode
is shown in Table 28. If the Power-down mode is activated
while in external program memory, the port data that is
held in the P2 SFR is restored to Port 2. If the data is a
logic 1, the port pin is held HIGH during the Power-down
mode by the strong pull-up transistor p1 (see Fig.13).
Table 28
Status of the external pins during Idle and Power-down modes
MODE
MEMORY
ALE
PSEN
PORT 0
PORT 1
PORT 2
PORT 3
Idle
Idle
Power-down
Power-down
internal
external
internal
external
1
1
0
0
1
1
0
0
port data
floating
port data
floating
port data
port data
port data
port data
port data
address
port data
port data
port data
port data
port data
port data