SCG9864 datasheet(5/27 Pages) ETC1

5 / 27 page

SCG9864

8-BIT MICROCONTROLLER

Score Concept Semiconductor Ltd.

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 64K bytes internal ROM with each page size is 16K bytes. 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 (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.

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