SMSC DS – TMC2005

Page 12

Rev. 10/24/2000

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.