MITSUBISHI MICROCOMPUTERS
4551 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER for
INFRARED REMOTE CONTROL TRANSMITTER
(5) Identification of the start condition
Warm start or cold start can be identified by examining the
state of the power down flag (P) with the SNZP instruction.
The warm start condition (timer 2 or external wakeup signal)
can be identified by examining the state of T2F flag.
POF instruction
or
POF2 instruction
Powerdown flag P
SQ
Reset input
R
q Set source
POF or POF2 instruction executed
q Clear source
Reset input
Fig. 34 Set source and clear source of the P flag
Software start
P = “1”
?
No
Cold start
Yes
Yes
T2F = “1”
?
No
Return by timer 2 Return by external
underflow
wakeup signal
Fig. 35 Start condition identified example using the SNZP instruction
(6) Return signal
An external wakeup signal or timer 2 interrupt request flag is
used to return from the clock operating mode.
An external wakeup signal is used to return from the RAM
back-up mode because the oscillation is stopped. Table 16
shows the return condition for each return source.
(7) Port P1 control register
q Pull-up control register PU0
Register PU0 controls the ON/OFF of the port P1 pull-up
transistor and the ON/OFF of the key-on wakeup function.
Set the contents of this register through register A with
the TPU0A instruction. In addition, the TAPU0 instruction
can be used to transfer the contents of register PU0 to
register A.
Table 16 Return source and return condition
Return source
Return condition
Remarks
Ports P0, P1 Returns by an external falling Port P0 shares the falling edge detection circuit with port P1. The key-on
edge input (“H”→“L”).
wakeup function of port P0 is always valid. The only key-on wakeup
function of the port P1 bit of which the pull-up transistor is turned on is
valid. Set all the port using the key-on wakeup function to “H” level before
going into the power down state.
Timer 2 interrupt Returns by timer 2 underflow and The timer 2 interrupt request flag (T2F) can be used only when system
request flag
setting T2F to “1.”
returns from the clock operating mode (POF instruction execution).
However, if the POF and POF2 instructions are executed while the T2F =
“1”, its operation is recognized as the return condition and system returns
from the clock operating mode.
Note: P1 pin has the pull-up transistor which can be turned on/off by software.
Table 17 Pull-up control register
Pull-up control register PU0
at reset : 00002
at power down : state retained
Port P13 pull-up transistor
PU03 control bit
0 Pull-up transistor OFF, no key-on wakeup
1 Pull-up transistor ON, key-on wakeup
Port P12 pull-up transistor
PU02 control bit
0 Pull-up transistor OFF, no key-on wakeup
1 Pull-up transistor ON, key-on wakeup
Port P11 pull-up transistor
PU01
control bit
0 Pull-up transistor OFF, no key-on wakeup
1 Pull-up transistor ON, key-on wakeup
Port P10 pull-up transistor
PU00 control bit
0 Pull-up transistor OFF, no key-on wakeup
1 Pull-up transistor ON, key-on wakeup
Note: “R” represents read enabled, and “W” represents write enabled.
R/W
34