em78p257 ELAN Microelectronics Corp, em78p257 Datasheet - Page 33

• Manufacturer Part Number: em78p257
• Description: 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

This specification is subject to change without prior notice.
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
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,
If Port 5 Input Status Change Interrupt is used to wake-up the EM78P257A/B, the following instructions must be
executed before SLEP:
(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.
[a] if Port 5 input status changed interrupt is enabled before SLEP , WDT must be disabled by
[b] if WDT is enabled before SLEP, Port 5 Input Status Change Interrupt must be disabled. Hence,
• Bit 7 of the IOCE0 register is set to "1", and the others are cleared.
• RF and IOCF0 register are cleared.
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.
the EM78P257A/B can be awakened only by Case 1 or 2. Refer to the section on Interrupt.
MOV A, @xx000110b
CONTW
CLR R1
MOV A, @xxxx1110b
CONTW
WDTC
MOV A, @0xxxxxxxb
IOW RE
MOV R5, R5
MOV A, @00000x1xb
IOW RF
ENI (or DISI)
SLEP
NOP
; Select internal TCC clock
; Clear TCC and prescaler
; Select WDT prescaler
; Clear WDT and prescaler
; Disable WDT
; Read Port 5
; Enable Port 5 input change interrupt
; Enable (or disable) global interrupt
; Sleep
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EM78P257
07.27.2004 (V1.4)
OTP ROM