SCG9910
8-BIT MICROCONTROLLER
Score Concept Semiconductor Ltd.
5
Sept 2000
Interrupt Mask Flag (I)
The flag will be set to 1 when entering an interrupt service routine. By that time,
all other interrupt events will be pending.
After exiting from the interrupt service routine, this interrupt mask flag will be
cleared to 0. Then interrupt handling will be resumed.
Memory
There are 48K bytes internal ROM with each page size of 16K bytes. However only a maximum
of 16K bytes area, the first page, can be used for coding. Besides, an extra 64 bytes area is for
interrupt vector addressing space. Regarding the instruction pointer, it is organized as iPAGE:PC
for instruction fetch.
Change of program flow between pages is by modifying the PAGE register and then followed by
executing a JMP or CALL instruction. These two instructions will load the PAGE register to
iPAGE and change the content in PC for long JMP or CALL instruction. It does not need to
change the PAGE register if it is a short JMP/CALL (i.e. JMP/CALL within page) because the
PAGE register is normally the same as the iPAGE register. To exit a subroutine, long or short
return type must be specified for long or short CALL respectively.
The microcontroller has 128 bytes internal RAM data storage of address $80-$FF. This area
includes stack frame and data memory. The stack frame is usually initialized at the highest RAM
address location, i.e. $FF.
Oscillation Circuits
Main system and subsystem oscillation circuitry generates the internal clock signal for the CPU
and other hardware timings. The main system clock uses the RC oscillation source. The
operating frequency is up to 4 MHz. This clock is for the CPU and the two timers.
The subsystem clock is for the real time signals. It uses 32.768 kHz crystal. It has to be tied to a
voltage level, either HIGH or LOW, if the real time timer and the watch dog timer are not used.
Power Down
The microcontroller supports power down mode for saving power.
Executing a STOP instruction will stop the main system oscillation to save most of
microcontroller power.
Only an external interrupt will release the microcontroller from STOP mode.
Interrupts
The MICROCONTROLLER has 2 timer interrupts, one real time interrupt, one external event
interrupt and one software interrupt. When interrupt occurs, the content of PC, iPAGE and PS
are pushed onto the stack in sequence. And then, the corresponding interrupt vector is loaded
into iPAGE:PC. Upon executing a RTI instruction, the registers are popped out of the stack in the
reversed order.
The preference of interrupt priority is Timer 0 / RTC interrupt, Timer 1 interrupt and then external
interrupt.
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
