NEC PD754144 - Manual (Page 222)

CHAPTER 8 STANDBY FUNCTION
222 User’s Manual U10676EJ3V0UM
8.3 Operation After Release of Standby Mode
(1) When the standby mode has been released by the RESET signal, the normal reset operation is performed.
(2) When the standby mode has been released by an interrupt, whether or not a vectored interrupt is executed
when the CPU has resumed instruction execution is determined by the contents of the interrupt master enable
flag (IME).
(a) When IME = 0
Execution is started from the instruction next to the one that set the standby mode after the standby mode
has been released. The interrupt request flag is retained.
(b) When IME = 1
A vector interrupt is executed after the standby mode has been released and then two instructions have
been executed. However, if the standby mode has been released by INT2 (testable input), servicing same
as (a) is performed because no vectored interrupt is generated in this case.
8.4 Application of Standby Mode
Use the standby mode according to the following procedure.
This example applies to the operation of the µPD754244 at f
X = 4.19 MHz. With f X = 6.0 MHz operation of the
µPD754244 and f
CC = 1.0 operation of the
µPD754144, the CPU clock and the wait time are different even if the settings
are the same.
<1> Detect the cause that sets the standby mode such as an interrupt input or power failure by port input.
<2> Process the I/O ports (process so that the current consumption is minimized).
Especially, do not leave the input ports open. Be sure to input a low or high level.
<3> Specify the interrupt that releases the standby mode.
<4> Specify the operation to be performed after the standby mode has been released (manipulate IME depending
on whether interrupt servicing is performed or not).
<5> Specify the CPU clock to be used after the standby mode has been released. (To change the clock, make
sure that the necessary machine cycles elapse before the standby mode is set.)
<6> Select the wait time to elapse after the standby mode has been released.
<7> Set the standby mode (by using the STOP or HALT instruction).