KS57C2308/P2308/C2316/P2316 OSCILLATOR CIRCUITS
6-5
POWER CONTROL REGISTER (PCON)
The power control register (PCON) is a 4-bit register that is used to select the CPU clock frequency and to
control CPU operating and power-down modes. The PCON can be addressed directly by 4-bit write instructions
or indirectly by the instructions IDLE and STOP.
FB3H PCON.3 PCON.2 PCON.1 PCON.0 PCON
PCON.3 and PCON.2 can be addressed only by the STOP and IDLE instructions, respectively, to engage the
idle and stop power-down modes. Idle and stop modes can be initiated by these instruction despite the current
value of the enable memory bank flag (EMB). PCON bits 1 and 0 can be written only by 4-bit RAM control
instruction. PCON is a write-only register. There are three basic choices:
—Main system clock (fx) or subsystem clock (fxt);
—Divided fx clock frequency of 4, 8, or 64
— Divided fxt clock frequency of 4.
PCON.1 and PCON.0 settings are also connected with the system clock mode control register, SCMOD. If
SCMOD.0 = "0", the main system clock is always selected by the PCON.1 and PCON.0 setting; if SCMOD.0 =
"1" the subsystem clock is selected.
RESET clears PCON register values (and SCMOD) to logic zero.
Table 6-1. Power Control Register (PCON) Organization
PCON Bit Settings Resulting CPU Clock Frequency
PCON.1 PCON.0 SCMOD.0 = 0 SCMOD.0 = 1
0 0 fx/64 fxt/4
1 0 fx/8
1 1 fx/4
PCON Bit Settings Resulting CPU Operating Mode
PCON.3 PCON.2
0 0 Normal CPU operating mode
0 1 IDLE
1 0 STOP mode