cx28250 Mindspeed Technologies, cx28250 Datasheet - Page 39

• Manufacturer Part Number: cx28250
• Description: Cx28250 Atm Physical Interface Phy Devices
• Manufacturer: Mindspeed Technologies

CX28250
ATM Physical Interface (PHY) Devices
2.1.1 PECL Interface
28250-DSH-002-C
2.1 Line Interface
The CX28250 communications with the external network through its line
interface. This is a Pseudo-Emitter Coupled Logic interface also referred to as a
Low Voltage PECL. This requires the same voltage differentials as on standard
Emitter Coupled Logic (ECL) devices but is referenced to a positive voltage
rather than ground. It uses the voltage differential to determine the logical value
as shown in
inputs of a PECL pair should be connected to ground or Vcc (one input to ground
and the other to Vcc). This prevents internal circuitry from toggling due to noise
on the inputs.
modulation as defined by the ATM Forum. It can connect to industry standard
Physical Media Dependent (PMD) devices for either fiber optic cable or Cat 5
UTP (unshielded twisted pair).
Table 2-1. PECL Input Logic Table
The selection of the correct PECL bias network is dependant on the PMD device
selected. For 3.3 Volt PMD's that can both source and sink current (that is they do
NOT put their outputs into a high Z condition for a logic 0). See
be set by an external resistor network, the designer should consult the PMD
manufacturer's data sheet and
This interface uses the Workable Interface Requirements Example (WIRE)
For PMD's that run at 5 volts or that require that the logic low output voltage
Input +
Mindspeed Technologies
0
0
1
1
Table
2-1. Absolute values are given in
Input -
Appendix A
0
1
0
1
™
of this document.
Section
Internal Logic Level
2.0 Functional Description
Invalid
Invalid
5.3. Note that unused
0
1
Figure 2-3
2.1 Line Interface
2-3