Texas Instruments TMS320 - Manual (Page 22)

TMS320 SECOND GENERATION
DIGITAL SIGNAL PROCESSORS
SPRS010B — MAY 1987 — REVISED NOVEMBER 1990
POST OFFICE BOX 1443

HOUSTON, TEXAS 77001 22
CLOCK CHARACTERISTICS AND TIMING
The TMS32020 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 fundamental
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.
PARAMETER TEST CONDITIONS MIN TYP † MAX UNIT
f
x
Input clock frequency T
A
= 0C to 70C 6.7 20.5 MHz
f
xs
Serial port frequency T
A
= 0C to 70C 50 † 2563 MHz
C1, C2 T
A
= 0C to 70C 10 pF
† Value derived from characterization data; minimum f
sx
at test = 825 kHz.
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 NOM MAX UNIT
t
c(C)
CLKOUT1/CLKOUT2 cycle time 195 597 ns
t
d(CIH-C)
CLKIN high to CLKOUT1/CLKOUT2/STRB high/low 25 60 ns
t
f(C)
CLKOUT1/CLKOUT2/STRB fall time 10 ns
t
r(C)
CLKOUT1/CLKOUT2/STRB rise time 10 ns
t
w(CL)
CLKOUT1/CLKOUT2 low pulse duration 2Q -- 15 2Q 2Q + 15 ns
t
w(CH)
CLKOUT1/CLKOUT2 high pulse duration 2Q -- 15 2Q 2Q + 15 ns
td(C1-C2) CLKOUT1 high to CLKOUT2 low, CLKOUT2 high to CLKOUT1 high, etc. Q -- 10 Q Q + 10 ns
NOTE 3: Q = 1/4t
c(C)
.
ADV
ANCE
INFORMA
T
ION