
1-4
DSP56007/D 
MOTOROLA
Signal/Connection Descriptions
Clock and PLL signals
CLOCK AND PLL SIGNALS
Note:
 While the PLL on this DSP is identical to the PLL described in the 
DSP56000 
Family Manual
, two of the signals have not been implemented externally. 
Specifically, there is no PLOCK signal or CKOUT signal available. Therefore, 
the internal clock is not directly accessible and there is no external indication 
that the PLL is locked. These signals were omitted to reduce the number of 
pins and allow this DSP to be put in a smaller, less expensive package.
Table 1-4   
Clock and PLL Signals  
Signal 
Name
Signal
Type
State 
during 
Reset
Signal Description
EXTAL
Input
Input
External Clock/Crystal
—This input should be connected to an 
external clock source. If the PLL is enabled, this signal is 
internally connected to the on-chip PLL. The PLL can multiply 
the frequency on the EXTAL pin to generate the internal DSP 
clock. The PLL output is divided by two to produce a four-phase 
instruction cycle clock, with the minimum instruction time being 
two PLL output clock periods. If the PLL is disabled, EXTAL is 
divided by two to produce the four-phase instruction cycle clock.
PCAP
Input
Input
PLL Filter Capacitor
—This input is used to connect a high-
quality (high “Q” factor) external capacitor needed for the PLL 
filter. The capacitor should be as close as possible to the DSP with 
heavy, short traces connecting one terminal of the capacitor to 
PCAP and the other terminal to V
CCP
. The required capacitor 
value is specified in 
Table 2-6
 on page 2-6.
Note:
When short lock time is critical, low dielectric absorption 
capacitors such as polystyrene, polypropylene, or teflon are 
recommended.
If the PLL is not used (i.e., it remains disabled at all times), there is 
no need to connect a capacitor to the PCAP pin. It may remain 
unconnected, or be tied to either V
cc
 or GND.
PLL Initialization (PINIT)
—During the assertion of hardware 
reset, the value on the PINIT line is written into the PEN bit of the 
PCTL register. When set, the PEN bit enables the PLL by causing 
it to derive the internal clocks from the PLL voltage controlled 
oscillator output. When the bit is cleared, the PLL is disabled and 
the DSP’s internal clocks are derived from the clock connected to 
the EXTAL signal. After hardware RESET is deasserted, the 
PINIT signal is ignored.
PINIT
Input
Input