4554 Datasheet, PDF (55/138 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4554 Group
POWER DOWN FUNCTION
The 4554 Group has 2-type power down functions.
System enters into each power down state by executing the follow-
ing instructions.
• Clock operating mode ...................... EPOF and POF instructions
• RAM back-up mode ....................... EPOF and POF2 instructions
When the EPOF instruction is not executed before the POF or
POF2 instruction is executed, these instructions are equivalent to
the NOP instruction.
(1) Clock operating mode
The following functions and states are retained.
• RAM
• Reset circuit
• XCIN–XCOUT oscillation
• LCD display
• Timer 5
(2) RAM back-up mode
The following functions and states are retained.
• RAM
• Reset circuit
(3) Warm start condition
The system returns from the power down state when;
• External wakeup signal is input
• Timer 5 underflow occurs
in the power down mode.
In either case, the CPU starts executing the software from address
0 in page 0. In this case, the P flag is “1.”
(4) Cold start condition
The CPU starts executing the software from address 0 in page 0
when;
• reset pulse is input to RESET pin,
• reset by watchdog timer is performed, or
• reset by the voltage drop detection circuit is performed.
In this case, the P flag is “0.”
(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 from the clock operating mode can be identified by exam-
ining the state of T5F flag.
Table 15 Functions and states retained at power down
Function
Power down mode
Clock
RAM
operating back-up
Program counter (PC), registers A, B,
✕
✕
carry flag (CY), stack pointer (SP) (Note 2)
Contents of RAM
Interrupt control registers V1, V2
O
O
✕
✕
Interrupt control registers I1, I2
O
O
Selected oscillation circuit
O
O
Clock control register MR
O
O
Timer 1 to timer 4 functions
(Note 3) (Note 3)
Timer 5 function
O
O
Timer LC function
Watchdog timer function
Timer control registers PA, W4
O
(Note 3)
✕ (Note 4) ✕ (Note 4)
✕
✕
Timer control registers W1 to W3, W5, W6
O
O
LCD display function
O
(Note 5)
LCD control registers L1 to L3
O
O
Voltage drop detection circuit
(Note 6) (Note 6)
Port level
(Note 7) (Note 7)
Pull-up control registers PU0, PU1
O
O
Key-on wakeup control registers K0 to K2
O
O
Port output format control registers
O
O
FR0 to FR2
External interrupt request flags
✕
✕
(EXF0, EXF1)
Timer interrupt request flags (T1F to T4F) (Note 3) (Note 3)
Timer interrupt request flag (T5F)
Interrupt enable flag (INTE)
Watchdog timer flags (WDF1, WDF2)
Watchdog timer enable flag (WEF)
O
O
✕
✕
✕ (Note 4) ✕ (Note 4)
✕ (Note 4) ✕ (Note 4)
Notes 1:“O” represents that the function can be retained, and “✕” repre-
sents that the function is initialized.
Registers and flags other than the above are undefined at RAM
back-up, and set an initial value after returning.
2: The stack pointer (SP) points the level of the stack register and is
initialized to “7” at RAM back-up.
3: The state of the timer is undefined.
4: Initialize the watchdog timer with the WRST instruction, and then
go into the power down state.
5: LCD is turned off.
6: When the SVDE instruction is executed while the VDCE pin is in
the “H“ state, this function is valid at power down.
7: In the power down mode, C/CNTR1 pin outputs “L” level.
However, when the CNTR input is selected (W11, W10=“11”), C/
CNTR1 pin is in an input enabled state (output=high-impedance).
Other ports retain their respective output levels.
Rev.3.00 Aug 06, 2004 page 55 of 136
REJ03B0043-0300Z