S3C8245/P8245/C8249/P8249 INTERRUPT STRUCTURE
5-9
SYSTEM MODE REGISTER (SYM)
The system mode register, SYM (set 1, DEH), is used to globally enable and disable interrupt processing and to
control fast interrupt processing (see Figure 5-5).
A reset clears SYM.1, and SYM.0 to "0". The 3-bit value for fast interrupt level selection, SYM.4–SYM.2, is
undetermined.
The instructions EI and DI enable and disable global interrupt processing, respectively, by modifying the bit 0 value of
the SYM register. In order to enable interrupt processing an Enable Interrupt (EI) instruction must be included in the
initialization routine, which follows a reset operation. Although you can manipulate SYM.0 directly to enable and
disable interrupts during the normal operation, it is recommended to use the EI and DI instructions for this purpose.
System Mode Register (SYM)
DEH, Set 1, R/W
.7 .6 .5 .4 .3 .2 .1 .0MSB LSB
Global interrupt enable bit:
0 = Disable all interrupts processing
1 = Enable all interrupts processing
Fast interrupt enable bit:
0 = Disable fast interrupts processing
1 = Enable fast interrupts processing
Fast interrupt level
selection bits:
0 0 0 = IRQ0
0 0 1 = IRQ1
0 1 0 = IRQ2
0 1 1 = IRQ3
1 0 0 = IRQ4
1 0 1 = IRQ5
1 1 0 = IRQ6
1 1 1 = IRQ7
Not used for the S3C8245/C8249
Figure 5-5. System Mode Register (SYM)