MPC8548CVTAQJ datasheet(61/144 Pages) FREESCALE

61 / 144 page

MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 6

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

Using this waveform, the definitions are as follows. To simplify the illustration, the following definitions

assume that the SerDes transmitter and receiver operate in a fully symmetrical differential signaling

environment.

1. Single-ended swing

The transmitter output signals and the receiver input signals SD_TX, SD_TX, SD_RX and SD_RX

each have a peak-to-peak swing of A – B volts. This is also referred as each signal wire’s

single-ended swing.

2. Differential output voltage, VOD (or differential output swing):

The differential output voltage (or swing) of the transmitter, VOD, is defined as the difference of

the two complimentary output voltages: VSD_TX –VSD_TX. The VOD value can be either positive

or negative.

3. Differential input voltage, VID (or differential input swing):

The differential input voltage (or swing) of the receiver, VID, is defined as the difference of the two

complimentary input voltages: VSD_RX –VSD_RX. The VID value can be either positive or

negative.

4. Differential peak voltage, VDIFFp

The peak value of the differential transmitter output signal or the differential receiver input signal

is defined as differential peak voltage, VDIFFp = |A – B| volts.

5. Differential peak-to-peak, VDIFFp-p

Since the differential output signal of the transmitter and the differential input signal of the receiver

each range from A – B to –(A – B) volts, the peak-to-peak value of the differential transmitter

output signal or the differential receiver input signal is defined as differential peak-to-peak voltage,

VDIFFp-p = 2 × VDIFFp = 2 × |(A – B)| volts, which is twice of differential swing in amplitude, or

twice of the differential peak. For example, the output differential peak-to-peak voltage can also be

calculated as VTX-DIFFp-p = 2 × |VOD|.

6. Common mode voltage, Vcm

The common mode voltage is equal to one half of the sum of the voltages between each conductor

of a balanced interchange circuit and ground. In this example, for SerDes output, Vcm_out = VSD_TX

+ VSD_TX = (A + B)/2, which is the arithmetic mean of the two complimentary output voltages

within a differential pair. In a system, the common mode voltage may often differ from one

component’s output to the other’s input. Sometimes, it may be even different between the receiver

input and driver output circuits within the same component. It is also referred to as the DC offset.

MPC8548CVTAQJ датащи(PDF) 61 Page - Freescale Semiconductor, Inc