Motorola DSP56012 - Manual (Page 79)

Memory, Operating Modes, and Interrupts
Phase Lock Loop (PLL) Configuration
MOTOROLA DSP56012 User’s Manual 3-19
3.7 PHASE LOCK LOOP (PLL) CONFIGURATION
Section 9 of the DSP56000 Family Manual provides detailed information about the
PLL. The information included here is a brief overview of the PLL.
The PLL is configured and controlled by bits in the PLL Control Register (PCTL). The
PLL Multiplication Factor and the clock applied to EXTAL determine the frequency
at which the Voltage Controlled Oscillator (VCO) will oscillate, that is, the output
frequency of the PLL.
If the PLL is used as the DSP internal clock (PCTL bit PEN = 1):
• the PLL VCO output is used directly as the internal DSP clock if the PCTL
Chip Clock Source Bit (CSRC) is set, and
• the PLL VCO frequency is divided by the Low Power Divider (LPD) and then
used as the internal DSP clock if the CSRC bit is cleared.
The DSP56012 PLL Multiplication Factor is set to 3 during hardware reset, which
means that the Multiplication Factor bits (MF1[1:0] in the PCTL) are set to $002. The
PLL may be disabled (PEN = 0) upon reset by pulling the PINIT pin low. The DSP
will subsequently operate at the frequency of the clock applied to the EXTAL pin
until the PEN bit is set. This reset value cannot be modified by the user until the DSP
comes out of Reset. The DSP56012 LPD Division Factor bits (DF[3:0] in the PCTL) are
cleared during hardware reset. Once the PEN bit is set, it cannot be cleared by
software.
P: $0052 DAX Block Transferred
P: $0054 Reserved
P: $0056 DAX Transmit Register Empty
P: $0058 Reserved
.
.
. .
.
.
P: $007E Reserved
Table 3-5 Interrupt Vectors (Continued)
Address Interrupt Source