Motorola DSP56301 - Manual (Page 95)

PLL Control Register (PCTL)
Core Configuration 4 -21
4.5 PLL Control Register (PCTL)
The bootstrap program must initialize the system Phase-Lock Loop (PLL) circuit by
configuring the PLL Control Register (PCTL). The PCTL is an X-I/O mapped, read/write
register that directs the on-chip PLL operation. (See Figure 4-5.)
Table 4-8 defines the DSP56301 PCTL bits. Changing the following bits may cause the PLL
to lose lock and re-lock according to the new value: PD[3–0], PEN, XTLR, and MF.
23 22 21 20 19 18 17 16 15 14 13 12
PD3 PD2 PD1 PD0 COD PEN PSTP XTLD XTLR DF2 DF1 DF0
11 10 9 8 7 6 5 4 3 2 1 0
MF11 MF10 MF9 MF8 MF7 MF6 MF5 MF4 MF3 MF2 MF1 MF0
Figure 4-5. PLL Control Register (PCTL)
Table 4-8. PLL Control Register (PCTL) Bit Definitions
Bit Number Bit Name Reset Value Description
23–20 PD[3–0] 0 Predivider Factor
Define the predivision factor (PDF) to be applied to the PLL input frequency.
The PD[3–0] bits are cleared during DSP56301 hardware reset, which
corresponds to a PDF of one.
19 COD 0 Clock Output Disable
Controls the output buffer of the clock at the CLKOUT pin. When COD is set,
the CLKOUT output is pulled high. When COD is cleared, the CLKOUT pin
provides a 50 percent duty cycle clock.
18 PEN Set to PINIT
input value
PLL Enable
Enables PLL operation.
17 PSTP 0 PLL Stop State
Controls PLL and on-chip crystal oscillator behavior during the stop
processing state.
16 XTLD 0 XTAL Disable
Controls the on-chip crystal oscillator XTAL output. The XTLD bit is cleared
during DSP56301 hardware reset, so the XTAL output signal is active,
permitting normal operation of the crystal oscillator.
15 XTLR 0 Crystal Range
Controls the on-chip crystal oscillator transconductance. The XTLR bit is
cleared (0) during hardware reset in the DSP56303.
14–12 DF[2–0] 0 Division Factor
Define the DF of the low-power divider. These bits specify the DF as a power
of two in the range from 2
0
to 2
7
.
11–0 MF[11–0] 0 PLL Multiplication Factor
Define the multiplication factor that is applied to the PLL input frequency. The
MF bits are cleared during DSP56301 hardware reset and thus correspond to
an MF of one.