SM39R08A5
8-Bit Micro-controller
with 8KB Flash
& 256B RAM embedded
9. Interrupt
The SM39R08A5 provides 9 interrupt sources with four priority levels. Each source has its own request flag(s) located in
a special function register. Each interrupt requested by the corresponding flag could individually be enabled or disabled
by the enable bits in SFR’s IEN0, and IEN1.
When the interrupt occurs, the engine will vector to the predetermined address as shown in Table 9.1. Once interrupt
service has begun, it can be interrupted only by a higher priority interrupt. The interrupt service is terminated by a return
from instruction RETI. When an RETI is performed, the processor will return to the instruction that would have been next
when interrupt occurred.
When the interrupt condition occurs, the processor will also indicate this by setting a flag bit. This bit is set regardless of
whether the interrupt is enabled or disabled. Each interrupt flag is sampled once per machine cycle, and then samples are
polled by hardware. If the sample indicates a pending interrupt when the interrupt is enabled, then interrupt request flag is
set. On the next instruction cycle the interrupt will be acknowledged by hardware forcing an LCALL to appropriate vector
address.
Interrupt response will require a varying amount of time depending on the state of microcontroller when the interrupt
occurs. If microcontroller is performing an interrupt service with equal or greater priority, the new interrupt will not be
invoked. In other cases, the response time depends on current instruction. The fastest possible response to an interrupt is
7 machine cycles. This includes one machine cycle for detecting the interrupt and six cycles for perform the LCALL.
Table 9-1: Interrupt vectors
Interrupt Vector
Interrupt Request Flags
Address
IE0 – External interrupt 0
0003h
TF0 – Timer 0 interrupt
000Bh
IE1 – External interrupt 1
0013h
TF1 – Timer 1 interrupt
001Bh
RI/TI – Serial channel interrupt
0023h
PWMIF – PWM interrupt
ADCIF – A/D converter interrupt
LVIIF – Low Voltage Interrupt
IICIF – IIC interrupt
WDTIF–WDT interrupt
Comparator interrupt
0043h
0053h
0063h
006Bh
008Bh
0093h
Interrupt Number
*(use Keil C Tool)
0
1
2
3
4
8
10
12
13
17
18
*See Keil C about C51 User’s Guide about Interrupt Function description
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M067
Ver B SM39R08A5 04/22/2013
- 33 -
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
