EM78P257
OTP ROM
• Bit 7 of the IOCE0 register is set to "1", and the others are cleared.
• RF and IOCF0 register are cleared.
The sleep (power down) mode is attained by executing the “ SLEP” instruction. While entering sleep mode, WDT
(if enabled) is cleared but keeps on running. The controller can be awakened by
(1) external reset input on /RESET pin.
(2) WDT time-out (if enabled).
(3) Port 5 input status changed (if enabled).
(4) Comparator status changed.
The first two cases will cause the EM78P257A/B to reset. The T and P flags of R3 can be used to determine the
source of the reset (wake-up). Case 3 is considered the continuation of program execution and the global interrupt
("ENI" or "DISI" being executed) decides whether or not the controller branches to the interrupt vector following
wake-up. If ENI is executed before SLEP, the instruction will begin to execute from the address 3FEH after
wake-up. If DISI is executed before SLEP, the operation will restart from the instruction right next to SLEP after
wake-up.
Only one of Cases 2 and 3 can be enabled before entering the sleep mode. That is,
[a] if Port 5 input status changed interrupt is enabled before SLEP , WDT must be disabled by
software. However, the WDT bit in the option register remains enabled. Hence, the
EM78P257A/B can be awakened only by Case 1 or 3. Similarly, the same procedures should be
applied if comparator status change interrupt is used. The device can be awakened only by Case
1 or 4.
[b] if WDT is enabled before SLEP, Port 5 Input Status Change Interrupt must be disabled. Hence,
the EM78P257A/B can be awakened only by Case 1 or 2. Refer to the section on Interrupt.
If Port 5 Input Status Change Interrupt is used to wake-up the EM78P257A/B, the following instructions must be
executed before SLEP:
MOV A, @xx000110b
CONTW
; Select internal TCC clock
CLR R1
MOV A, @xxxx1110b
CONTW
; Clear TCC and prescaler
; Select WDT prescaler
WDTC
MOV A, @0xxxxxxxb
IOW RE
; Clear WDT and prescaler
; Disable WDT
MOV R5, R5
; Read Port 5
MOV A, @00000x1xb
IOW RF
; Enable Port 5 input change interrupt
ENI (or DISI)
SLEP
; Enable (or disable) global interrupt
; Sleep
NOP
This specification is subject to change without prior notice.
33
07.27.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
