TMS320UC5405 Datasheet, PDF (45/77 Pages) Texas Instruments – Fixed-Point Digital Signal Processor

Electrical Specifications
6.5 Clock Options
The frequency of the reference clock provided at the CLKIN pin can be divided by a factor of two or four or
multiplied by one of several values to generate the internal machine cycle.
6.5.1 Internal Oscillator With External Crystal
The internal oscillator is enabled by connecting a crystal across X1 and X2/CLKIN. The frequency of CLKOUT
is a multiple of the oscillator frequency. The multiply ratio is determined by the bit settings in the CLKMD
register. The crystal should be in fundamental-mode operation, and parallel resonant, with an effective series
resistance of 30 Ω and power dissipation of 1 mW. The circuit shown in Figure 6−2 represents
fundamental-mode operation.
The connection of the required circuit, consisting of the crystal and two load capacitors, is shown in Figure 6−2.
The load capacitors, C₁ and C₂, should be chosen such that the equation below is satisfied. C_L in the equation
is the load specified for the crystal.
C_L
+
C₁C₂
(C₁ ) C₂)
f_clock Input clock frequency
MIN MAX UNIT
10 20
MHz
X1
C1
X2/CLKIN
Crystal
C2
Figure 6−2. Internal Oscillator With External Crystal
October 2002 − Revised October 2004
SPRS199B
45