AM7968 datasheet(103/127 Pages) AMD

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TAXIchip Integrated Circuits Technical Manual

TAXI Technical Information Publication #89-05

Subject: TAXIchip Set Crystal Specification

Question:

What are the design considerations for crystals used with TAXIchip set?

Answer:

The TAXIchip’s parallel mode oscillator uses a 4.0 MHz – 17.5 MHz crystal with a

frequency tolerance of 0.1%.

Any crystal will oscillate in either series or parallel mode depending upon the type of

oscillator used. By specifying parallel mode and the load, the manufacturer will calibrate

the crystal in parallel mode at the desired frequency. This could be important in

applications where frequency tolerance is critical due to the fact that the resonant

frequency in parallel mode is typically 0.02% above the series mode frequency.

As discussed in section 3.3, the time required to synchronize the data recovery circuit in

the Receiver is proportional to the delta between the Transmitter frequency and the

Receiver PLL resting frequency. The Receiver resting frequency is typically less than

±1% away from its own crystal frequency, due to mismatch between internal circuits.

The crystal specification of 0.1% is meant to be small enough to cause a negligible

effect on lock time while not increasing the crystal cost (0.025% crystals are quite

common). Sometimes tighter frequency and tolerance specifications may be necessary

to meet the user’s system requirements (i.e. FIFO depth, etc.).

More information on crystal specifications for the TAXIchip set may be found in

Section 4.1.1.

A partial list of vendors follows:

Typical 12.5 MHz

Distributor

Part Number

Phone Number

I.E.A.

HC18U 12.500

(408) 435-1000

Calmax Corp.

UM-12.5

(714) 957-1299

Monitor Products

MM 49XlE12A-12.5

(619) 433-4510

Anderson Electronics

011-668-03260

(814) 695-4428

Target Electronics

CC025A-12.5

(408) 733-0384

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