CONTROL REGISTERS
S3C80A5B
4-26
SYM
— System Mode Register
DEH
Set 1
Bit Identifier
.7
.6
.5
.4
.3
.2
.1
.0
RESET Value
0
–
–
x
x
x
0
0
Read/Write
R/W
–
–
R/W
R/W
R/W
R/W
R/W
Addressing Mode
Register addressing mode only
.7
Tri-State External Interface Control Bit
(1)
0
Normal operation (disable tri-state operation)
1
Set external interface lines to high impedance (enable tri-state operation)
.6–.5
Not used for S3C80A5B.
.4–.2
Fast Interrupt Level Selection Bits
(2)
0
0
0
IRQ0
0
0
1
IRQ1
0
1
0
Not used for
0
1
1
S3C80A5B.
1
0
0
1
0
1
1
1
0
IRQ6
1
1
1
IRQ7
.1
Fast Interrupt Enable Bit
(3)
0
Disable fast interrupt processing
1
Enable fast interrupt processing
.0
Global Interrupt Enable Bit
(4)
0
Disable global interrupt processing
1
Enable global interrupt processing
NOTES
:
1. Because an external interface is not implemented for the S3C80A5B, SYM.7 must always be "0".
2. You can select only one interrupt level at a time for fast interrupt processing.
3. Setting SYM.1 to "1" enables fast interrupt processing for the interrupt level currently selected by SYM.2–SYM.4.
4.
Following a reset, you must enable global interrupt processing by executing an EI instruction (not by writing a "1"
to SYM.0).