CD1865 datasheet(47/150 Pages) INTEL

47 / 150 page

Intelligent Eight-Channel Communications Controller — CD1865

Datasheet

6.1

System Interface Considerations

When using the CD1865, two areas where system architects, designers, and programmers should

consider options are system clock speed, and unclocked versus clocked-host bus interface.

6.2

System Clock and Bit Rate Options

6.2.1

System Clock

System clock is a high-frequency clock (supplied by the user) used by the CD1865 to receive all

the necessary timing. The CD1865 is capable of handling system clock levels of TTL-compatible

voltage swings; however, the VIL and VIH specifications are not identical to all families of TTL

logic. Specifically, the clock signal (and the reset signal) have lower VIL and higher VIH than the

worst-case specifications of some TTL families. In general, any TTL family is adequate if not

heavily loaded. Refer to the DC Specifications in Section 10.3 for details.

××××××The CD1865 can be operated from the main system clock or its own clock. Operation from

the main system clock can reduce the number of clocks required, and it allows the bus interface

between the system and the CD1865 to be clocked, but in general, typical system clock speeds are

not exact baud-rate multiples. As bit rates are received from the clock, it is important to consider

this when selecting a clock value. If exact baud rates are needed, or the system clock is not a

convenient value, the CD1865 must be supplied with its own clock or crystal.

6.2.2

External Clock

It is recommended that the 2

×-clock option (oscillator or crystal) be used wherever possible. Figure

15 shows a possible design configuration for the clock circuitry if the crystal is being used. Please

refer to the CD1865 Evaluation Kit documentation for details on the design configurations used.

The crystal used for the evaluation board is a 66-MHz third overtone part.

Figure 15. 2

× Clock Option

OSC 2

OSC 1

200K–500K

33 pF

CD1865 Datasheet(PDF) 47 Page - Intel Corporation