CS61581 datasheet(24/37 Pages) CIRRUS

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CS61581

DS211PP8

4. ARBITRARY WAVEFORM

GENERATION

In addition to the predefined pulse shapes, the user

can create custom pulse shapes using the host

mode. This flexibility allows the board designer to

accommodate non-standard cables, EMI filters,

protection circuitry, etc.

The arbitrary pulse shape of mark (a transmitted 1)

is specified by describing it’s pulse shape across

three Unit Intervals (UIs). This allows, for exam-

ple, the long-haul return-to-zero tail to extend into

the next UI, or two UIs, as is required for isolated

pulses.

Each UI is divided into multiple phases, and the us-

ers defines the amplitude of each phase. The wave-

form of a space (a transmitted 0) is fixed at zero

volts. Examples of the phases are shown in

Figure 13. In all cases, to define an arbitrary wave-

form, the user writes to the Waveform Register ei-

ther 36, 39 or 42 times (12, 13 or 14 phases per UI

for three UIs). The phases are written in the order:

UI1/phase1,

UI1/phase2,...,

UI1/phase14,

UI2/phase1,...,

UI2/phase14,

UI3/phase1,...,

UI3/phase14.

For E1, short haul applications the CS61581 di-

vides the 488 ns UI into 12 uniform phases (40.7 ns

each), and will ignore the phase amplitude informa-

tion written for phases 13 and 14 of each UI.

For DSX-1 and DS1 applications, the CS61581 di-

vides the 648 ns UI into 13 uniform phases (49.8 ns

each), and will ignore the phase amplitude informa-

tion written for phase 14 of each UI.

For E1 long haul applications, the CS61581 divides

the 648 ns UI into 14 uniform phases (46.3 ns

each), and uses the phase information written for

all 14 phases of each UI.

When transmitting pulses, the CS61581 will add

the amplitude information from the prior two sym-

bols with the amplitude of the first UI of the current

symbol before outputting a signal on TTIP/TRING.

Therefore, a mark preceded by two spaces will be

output exactly as the mark is programmed. Howev-

er, when one mark is preceded by marks, the first

portion of the last mark may be modified. With

AMI data, where successive pulses have opposite

polarity, the undershoot tail of one pulse will cause

the rising edge of the next mark to rise more quick-

ly, as shown in Figure 14.

The amplitude of each phase is described by a 7-bit,

two’s compliment number, where a positive value

describes pulse amplitude, and a negative value de-

scribes pulse undershoot. The positive full value is

0x3F. The negative full value is 0x40. For T1, the

typical output voltage is 38 mV/LSB. For E1 coax,

the typical output voltage is 22 mV/LSB. For E1

shielded twisted pair, the typical output voltage is

E1 Arbitrary Waveform Example

DSX-1 (54% duty cycle) Arbitrary Waveform Example

DS-1 (50% duty cycle) Arbitrary Waveform Example

Figure 13. Phase Definition of Arbitrary Waveforms

CS61581

DS211F1

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