IDT82P2821 datasheet(39/152 Pages) RENESAS

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IDT82P2821

21(+1) CHANNEL HIGH-DENSITY T1/E1/J1 LINE INTERFACE UNIT

Functional Description

February 6, 2009

3.3.5

LINE DRIVER

The Line Driver can be set to High-Z for protection or in redundant

applications.

The following two ways will set the Line Driver to High-Z:

• Setting the OE pin to low will globally set all the Line Drivers to

High-Z;

• Setting the OE bit (b6, TCF0,...) to ‘0’ will set the corresponding

Line Driver to High-Z.

By these ways, the functionality of the internal circuit is not affected

and TTIPn and TRINGn will enter High-Z state immediately.

3.3.5.1 Transmit Over Current Protection

The Line Driver monitors the Transmit Over Current (TOC) on the

line interface. When TOC is detected, the driver’s output (i.e., output on

TTIPn/TRINGn) is determined by the THZ_OC bit (b4, TCF0,...). If the

THZ_OC bit (b4, TCF0,...) is ‘0’, the driver’s output current (peak to

peak) is limited to 100 mA; if the THZ_OC bit (b4, TCF0,...) is ‘1’, the

driver’s output will enter High-Z. TOC is indicated by the TOC_S bit (b4,

STAT0,...). A transition from ‘0’ to ‘1’ on the TOC_S bit (b4, STAT0,...) or

any transition (from ‘0’ to ‘1’ or from ‘1’ to ‘0’) on the TOC_S bit (b4,

STAT0,...) will set the TOC_IS bit (b4, INTS0,...) to ‘1’, as selected by the

TOC_IES bit (b4, INTES,...). When the TOC_IS bit (b4, INTS0,...) is ‘1’,

an interrupt will be reported by INT if not masked by the TOC_IM bit (b4,

INTM0,...).

TOC may be indicated by the TMFn pin. Refer to Section 3.5.7.2

TMFn Indication for details.

3.3.6

TX TERMINATION

The transmit line interface supports Transmit Differential mode and

Transmit Single Ended mode, as selected by the T_SING bit (b3,

TCF0,...). In Transmit Differential mode, both TTIPn and TRINGn are

used to transmit signals to the line side. In Transmit Single Ended mode,

only TTIPn is used to transmit signal.

The line interface can be connected with T1 100

Ω, J1 110 Ω or E1

120

Ω twisted pair cable or E1 75 Ω coaxial cable.

The transmit impedance matching is realized by using internal

impedance matching or external impedance matching for each channel

in different applications.

3.3.6.1 Transmit Differential Mode

In Transmit Differential mode, different applications have different

impedance matching. For T1/J1 applications, only Internal Impedance

Matching is supported. For E1 applications, both Internal and External

Impedance Matching are supported.

Internal Impedance Matching circuit uses an internal programmable

resistor (IM) only.

External Impedance Matching circuit uses an external resistor (Rt)

only.

A twisted pair cable can be connected with a 1:2 (step up) trans-

former or without a transformer (transformer-less), while a coaxial cable

must be connected with a 1:2 transformer.

The T_TERM[2:0] bits (b2~0, TCF0,...) should be set according to

different cable conditions, whether a transformer is used, and what kind

of Impedance Matching is selected.

Table-15 lists the recommended impedance matching value in

different applications. Figure-19 to Figure-21 show the connection for

one channel in different applications.

The transformer-less connection will offer a termination option with

reduced cost and board space. However, the waveform amplitude is not

standard compliant, and surge protection and common mode depres-

sion should be enhanced depending on equipment environment..

Table-15 Impedance Matching Value in Transmit Differential Mode

Cable Condition

Internal Impedance Matching

External Impedance Matching

T_TERM[2:0]

T1 100

Ω twisted pair (with transformer)

000

(not supported)

J1 110

Ω twisted pair (with transformer)

001

E1 120

Ω twisted pair (with transformer), PULS[3:0]=0001

010

111

Ω

E1 75

Ω coaxial (with transformer), PULS[3:0]=0000

011

T1 100

Ω twisted pair (transformer-less)

100

(not supported)

J1 110

Ω twisted pair (transformer-less)

101

E1 120

Ω twisted pair (transformer-less), PULS[3:0]=0001

110

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