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TMC2005-JT

ARCNET 5 Port HUB Controller

SMSC -> Microchip 

ARCNET 5 Port HUB Controller

Datasheet

Option Feature for Jitter Filtering

When any RX ports receive the bigger jitter than its allowance, the TMC2005 may fail to receive the data

correctly and the network may be down.. However the below method to escape is effective for the case that a

momentary big jitter occurs under a special condition like an optical transceiver.

1) Big jitter (BJ) mode

The reference phase of the internal DPLL is changed from the first pulse to the second pulse by setting “0” to the big

jitter mode pins (nBJX). This setup is effective for the case that a big jitter occurs when rising up from DC state as

same as when using an optical transceiver with ATC function (refer to complement).

Note: The delay time of the TMC2005 becomes 400nS (at 2.5Mbps) longer than the normal mode. The delay time

limits the maximum cable length and maximum node number.

[Complement] The big jitter may occur in the case of using an optical transceiver, especially an optical receiver that

has an ATC circuit that controls threshold level in proportion to received light strength. The first pulse especially after

long time idle has the big jitter but the second pulse is stabilized.

2) Changing polar of RX port

In order to filter the jitter of edge in one side, it is effective to set reverse to pin SA, SB, SE to change the polarity of

RX port.

Note: Changing the polarity of RX port makes the delay time of the TMC2005 circuit a half bit (200nS) longer than

original 2.5Mbps, and the delay time affects the maximum cable length and maximum node number.

Option Feature for Noise Cut mode

The Noise cut mode is enabled by setting pin nMBx sets 0. The noise cut mode is a function to remove the ringing

noise and the reflection noise generated on the leading edge side of the input pulse to receive data input RXINx. The

position and the width of the “dead band” are shown in the figure below.

- Dead band at Normal mode (nMBx=1)

Period of data rate (Tdr)

Tdr/8 = 1 clock

- Dead band at Noise cut mode (nMBx=0)

Period of data rate (Tdr)

Tdr/8 = 1 clock

RXIN

(Active High)

Ideal waveform

dead band

RXIN edge reference position:

Generated by adjacent phase of SYNC character (1,1,0)

RXIN

(Active High)

Ideal waveform

dead band: Noise cut band

RXIN edge reference position:

Generated by adjacent phase of SYNC character (1,1,0)

SMSC TMC2005-JT

Page 11

DATASHEET

Revision 1.0 (01-30-06)

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