3 System services

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3

System services

System services include all the necessary logic to start up and maintain the IMS C011.

3.1

Power

Power is supplied to the device via the VDD and GND pins. The supply must be decoupled close to the

chip by at least one 100 nF low inductance (e.g. ceramic) capacitor between VDD and GND. Four layer

boards are recommended; if two layer boards are used, extra care should be taken in decoupling.

AC noise between VDD and GND must be kept below 200 mV peak to peak at all frequencies above

100 KHz. AC noise between VDD and the ground reference of load capacitances must be kept below

200 mV peak to peak at all frequencies above 30 MHz. Input voltages must not exceed specification with

respect to VDD and GND, even during power-up and power-down ramping, otherwise

latchup can occur.

CMOS devices can be permanently damaged by excessive periods of latchup.

3.2

CapMinus

The internally derived power supply for internal clocks requires an external low leakage, low inductance

1

mF capacitor to be connected between VDD and CapMinus. A ceramic capacitor is preferred, with an

impedance less than 3 Ohms between 100 KHz and 10 MHz. If a polarised capacitor is used the negative

terminal should be connected to CapMinus. Total PCB track length should be less than 50 mm. The posi-

tive connection of the capacitor must be connected directly to VDD. Connections must not otherwise touch

power supplies or other noise sources.

Phase–locked

loops

VDD

GND

CapMinus

P.C.B track

P.C.B track

Decoupling

capacitor 1

mF

pin

VDD

Figure 3.1

Recommended PLL decoupling

3.3

ClockIn

Transputer family components use a standard clock frequency, supplied by the user on the ClockIn input.

The nominal frequency of this clock for all transputer family components is 5 MHz, regardless of device

type, transputer word length or processor cycle time. High frequency internal clocks are derived from

ClockIn, simplifying system design and avoiding problems of distributing high speed clocks externally.

A number of transputer family devices may be connected to a common clock, or may have individual clocks

providing each one meets the specified stability criteria. In a multi-clock system the relative phasing of

ClockIn clocks is not important, due to the asynchronous nature of the links. Mark/space ratio is unimpor-

tant provided the specified limits of ClockIn pulse widths are met.

Oscillator stability is important. ClockIn must be derived from a crystal oscillator; RC oscillators are not

sufficiently stable. ClockIn must not be distributed through a long chain of buffers. Clock edges must be

monotonic and remain within the specified voltage and time limits.