KS57C2308/P2308/C2316/P2316 OSCILLATOR CIRCUITS
6-11
Table 6-6. Elapsed Machine Cycles During CPU Clock Switch
AFTER SCMOD.0 = 0 SCMOD.0 = 1
BEFORE PCON.1 = 0 PCON.0 = 0 PCON.1 = 1 PCON.0 = 0 PCON.1 = 1 PCON.0 = 1
PCON.1 = 0 N/A 1 MACHINE CYCLE 1 MACHINE CYCLE
PCON.0 = 0
SCMOD.0 = 0 PCON.1 = 1 8 MACHINE CYCLES N/A 8 MACHINE CYCLES N/A
PCON.0 = 0
PCON.1 = 1 16 MACHINE CYCLES 16 MACHINE CYCLES N/A fx/4fxt
MACHINE
CYCLE
PCON.0 = 1
SCMOD.0 = 1 N/A N/A fx/4fxt (M/C) N/A
NOTES:
1. Even if oscillation is stopped by setting SCMOD.3 during main system clock operation, the stop mode is not entered.
2. Since the XIN input is connected internally to VSS to avoid current leakage due to the crystal oscillator in stop mode, do
not set SCMOD.3 to "1" or STOP instruction when an external clock is used as the main system clock.
3. When the system clock is switched to the subsystem clock, it is necessary to disable any interrupts which may occur
during the time intervals shown in Table 6-6.
4. “N/A” means “not available”.
5. fx: Main–system clock, fxt: Sub–system clock, M/C: Machine Cycle.
When fx is 4.19 MHz, and fxt is 32.768 kHz.
++ PROGRAMMING TIP — Switching Between Main System and Subsystem Clock
1. Switch from the main system clock to the subsystem clock:
MA2SUB BITS SCMOD.0 ;Switches to subsystem clock
CALL DLY80 ;Delay 80 machine cycles
BITS SCMOD.3 ;Stop the main system clock
RET
DLY80 LD A,#0FH
DEL1 NOP
NOP
DECS A
JR DEL1
RET
2. Switch from the subsystem clock to the main system clock:
SUB2MA BITR SCMOD.3 ;Start main system clock oscillation
CALL DLY80 ;Delay 80 machine cycles
CALL DLY80 ;Delay 80 machine cycles
BITR SCMOD.0 ;Switch to main system clock
RET