Texas Instruments TMS320 - Manual (Page 28)

TMS320 SECOND GENERATION
DIGITAL SIGNAL PROCESSORS
SPRS010B — MAY 1987 — REVISED NOVEMBER 1990
POST OFFICE BOX 1443

HOUSTON, TEXAS 77001 28
CLOCK CHARACTERISTICS AND TIMING
The TMS32025 can use either its internal oscillator or an external frequency source for a clock.
internal clock option
The internal oscillator is enabled by connecting a crystal across X1 and X2/CLKIN (see Figure 2). The frequency
of CLKOUT1
is one-fourth the crystal fundamental frequency. The crystal should be either fundamental
or overtone mode, and parallel resonant, with an effective series resistance of 30 , a power dissipation
of 1 mW, and be specified at a load capacitance of 20 pF. Note that overtone crystals require an additional tuned
LC circuit; see the application report, Hardware Interfacing to the TMS320C25 (SPRA014A).
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
f
x
Input clock frequency T
A
= 0C to 70C 6.7 40.96 MHz
f
xs
Serial port frequency T
A
= 0C to 70C 0 † 5120 MHz
C1, C2 T
A
= 0C to 70C 10 pF
† The serial port was tested at a minimum frequency of 1.25 MHz. However, the serial port was fully static but will properly function down
to f
sx
= 0 Hz.
X2/CLKIN
C2 C1
X1
Crystal
Figure 2. Internal Clock Option
external clock option
An external frequency source can be used by injecting the frequency directly into X2/CLKIN with X1 left
unconnected. The external frequency injected must conform to the specifications listed in the following table.
switching characteristics over recommended operating conditions (see Note 3)
PARAMETER MIN TYP MAX UNIT
t
c(C)
CLKOUT1/CLKOUT2 cycle time 97.7 597 ns
t
d(CIH-C)
CLKIN high to CLKOUT1/CLKOUT2/STRB high/low 5 30 ns
t
f(C)
CLKOUT1/CLKOUT2/STRB fall time 5 ns
t
r(C)
CLKOUT1/CLKOUT2/STRB rise time 5 ns
t
w(CL)
CLKOUT1/CLKOUT2 low pulse duration 2Q -- 8 2Q 2Q + 8 ns
t
w(CH)
CLKOUT1/CLKOUT2 high pulse duration 2Q -- 8 2Q 2Q + 8 ns
t
d(C1-C2
) CLKOUT1 high to CLKOUT2 low, CLKOUT2 high to CLKOUT1 high, etc. Q -- 5 Q Q + 5 ns
NOTE 3: Q = 1/4t
c(C)
.
ADV
ANCE
INFORMA
T
ION