TMS320 datasheet(28/69 Pages) TI

28 / 69 page

TMS320C25, TMS320E25

SPRS010B — MAY 1987 — REVISED NOVEMBER 1990

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77001

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

Ω, 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

Input clock frequency

TA = 0°C to 70°C

6.7

40.96

MHz

fxs

Serial port frequency

TA = 0°C to 70°C

0 †

5 120

MHz

C1, C2

TA = 0°C to 70°C

† 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 fsx = 0 Hz.

X2/CLKIN

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

tc(C)

CLKOUT1/CLKOUT2 cycle time

97.7

597

td(CIH-C)

CLKIN high to CLKOUT1/CLKOUT2/STRB high/low

tf(C)

CLKOUT1/CLKOUT2/STRB fall time

tr(C)

CLKOUT1/CLKOUT2/STRB rise time

tw(CL)

CLKOUT1/CLKOUT2 low pulse duration

2Q – 8

2Q + 8

tw(CH)

CLKOUT1/CLKOUT2 high pulse duration

2Q – 8

2Q + 8

td(C1-C2)

CLKOUT1 high to CLKOUT2 low, CLKOUT2 high to CLKOUT1 high, etc.

Q – 5

Q + 5

NOTE 3: Q = 1/4tc(C).

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