33
8Bit Single Chip Microcontroller
DMC73C168
FSELn
:
BEEP Frequency select :
FSEL1 FSEL0
BEEP FREQ.
0
0
1
1
0
1
0
1
417Hz
1KHz
(2/3 Duty)
(1/2 Duty)
1.25 KHz (1/2 Duty)
2.5 KHz (1/2 Duty)
9) Peripheral RAM register
PF NAME : PRAM 0-127
: Peripheral RAM register
P64-P191 R/W
>140 ~ READ
>01BF WRITE
RESET VALUE
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
X
BIT 1
BIT 0
X
Peripheral RAM register
Peripheral RAM register
X
X
X
X
X
X
These peripheral RAM region is >140 (hex) to >01BF (hex), and size is 128 bytes.
4.8 Interrupt and Reset Priorities
The DMC73C168 has priority servicing of interrupt levels and RESET. These levels are defined as
shown in Table 4-8. The TRAP instruction branch to a two bytes location in a reserved section of
memory called the TRAP Vector Table. As shown in Figure 4-8, each trap location stores a 16-bit
address which references either reset function (TRAP0), one of the seven interrupt service routine
(TRAP1-INT1, TRAP2-INT2, TRAP3-INT3, TRAP4-INT4, TRAP5-INT5, TRAP6-INT6, TRAP7-INT7),
or a subroutine (TRAP8-23).
Once INTn has been acknowledged by the CPU, the corresponding INTn Flag flip flop is cleared.
The CPU then pushes the contents of the Status Register and Program Counter (MSB and LSB)
onto the stack and zeros the Status Register, including the global Interrupt Enable (I) bit. the CPU
reads an interrupt code from the interrupt logic and branches to the address contained in the
corresponding interrupt vector location in memory.
The interrupt service routine can explicitly enable nested interrupt by executing the EINT instruction
to directly set I bit in the Status Register to a one, thus permitting nested interrupt to be recognized.
When the nested interrupt service routine completes, it returns to the previous interrupt service
routine by executing the RETI instruction.
Level
Name
Trigger Factor
Vector
MSB LSB
0
1
RESET
Active Low/Level Sensitive
Program Selectable
>FFFE >FFFF
>FFFC >FFFD
>FFFA >FFFB
>FFF8 >FFF9
>FFF6 >FFF7
INT1 External (CE)
INT2 Timer 1
2
Timer 1 through '>0000'
Program Selectable
3
INT3 External
INT4 External
4-0
Program Selectable
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