XC886/888CLM
Processor Architecture
User’s Manual
2-6
V1.3, 2010-02
Processor Architecture, V 1.0
2.2.7
Power Control (PCON)
The CPU has two power-saving modes: idle mode and power-down mode. The idle
mode can be entered via the PCON register. In idle mode, the clock to the CPU is
stopped while the timers, serial port and interrupt controller continue to run using a
half-speed clock. In power-down mode, the clock to the entire CPU is stopped.
2.3
Instruction Timing
For memory access without wait state, a CPU machine cycle comprises two input clock
periods referred to as Phase 1 (P1) and Phase 2 (P2) that correspond to two different
CPU states. A CPU state within an instruction is denoted by reference to the machine
cycle and state number, e.g., C2P1 is the first clock period within machine cycle 2.
Memory accesses take place during one or both phases of the machine cycle. SFR
writes only occur at the end of P2. An instruction takes one, two or four machine cycles
to execute. Registers are generally updated and the next opcode read at the end of P2
of the last machine cycle for the instruction.
With each access to the Flash memory, instruction execution times are extended by one
machine cycle (one wait state), starting from either P1 or P2.
shows the fetch/execute timing related to the internal states and phases.
Execution of an instruction occurs at C1P1. For a 2-byte instruction, the second reading
starts at C1P1.
PCON
Power Control Register
Reset Value: 00
H
7
6
5
4
3
2
1
0
SMOD
0
GF1
GF0
0
IDLE
rw
r
rw
rw
r
rw
Field
Bits
Type Description
IDLE
0
rw
Idle Mode Enable
0
Do not enter idle mode
1
Enter idle mode
GF0
2
rw
General Purpose Flag Bit 0
GF1
3
rw
General Purpose Flag Bit 1
0
1,
[6:4]
r
Reserved
Returns 0 if read; should be written with 0.
*
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