4507_M Datasheet, PDF (162/216 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4507 Group
APPLICATION
2.6 RAM back-up
2.6.3 Notes on use
(1) Key-on wakeup function
After setting ports (P0, P1, D2/C, D3/K, P20/AIN0 and P21/AIN1 specified with register K0–K2) which
key-on wakeup function is valid to “H,” execute the POF2 instruction.
If one of ports which key-on wakeup function is valid is in the “L” level state, system returns from
the RAM back-up after the POF2 instruction is executed.
(2) POF2 instruction
Execute the POF2 instruction immediately after executing the EPOF instruction to enter the RAM
back-up state.
Note that system cannot enter the RAM back-up state when executing only the POF2 instruction.
Be sure to disable interrupts by executing the DI instruction before executing the EPOF instruction
and the POF2 instruction.
(3) Return from RAM back-up
After system returns from RAM back-up, set the undefined registers and flags.
The initial value of the following registers are undefined at RAM back-up. After system is returned
from RAM back-up, set initial values.
• Register Z (2 bits)
• Register X (4 bits)
• Register Y (4 bits)
• Register D (3 bits)
• Register E (8 bits)
(4) Watchdog timer
The watchdog timer function is valid after system is returned from the RAM back-up. When not using
the watchdog timer function, execute the DWDT instruction and the WRST instruction continuously
every system is returned from the RAM back-up, and stop the watchdog timer function.
(5) P13/INT pin
When the bit 3 of register I1 is cleared, the RAM back-up mode is selected and the input of INT pin
is disabled, be careful about the following notes.
• When the key-on wakeup function of port P13 is not used (register K13 = “0”), clear bits 2 and 3
of register I1 before system enters to the RAM back-up mode.
(6) External clock
When the external signal clock is used as the source oscillation (f(XIN)), note that the RAM back-
up mode (POF2 instruction) cannot be used.
Rev.2.01 Feb 04, 2005
REJ09B0195-0201
2-47