CS61880 datasheet(42/70 Pages) CIRRUS

42 / 70 page

CS61880

DS450PP3

15. ARBITRARY WAVEFORM

GENERATOR

Using the Arbitrary Waveform Generator (AWG)

allows the user to customize the transmit pulse

shapes to compensate for nonstandard cables,

transformers, protection circuitry, or to reduce

power consumption by reducing the output pulse

amplitude. A channel is configured for a custom

pulse shape by enabling the AWG for that channel

and then storing data representing the pulse shape

into the 24 phase sample locations. Each channel

has a separate AWG, so all eight channels can have

a different customized pulse shape. The micropro-

cessor interface, is used to read from or write to the

AWG, while the device is in host mode.

In the AWG RAM, the pulse shape is divided into

two unit intervals (UI). There are 12 phase sample

addresses in each UI. The first UI is for the main

part of the pulse and the second UI is for the “tail”

of the pulse (Refer to Figure 13). A complete pulse-

shape is represented by 24 phase samples. Data

written in the first UI represents a valid pulse

shape, while data in the second UI must be set to

zero at all times. Writing values other that zero to

the second UI will cause the pulse shape to be in-

valid.

The data in each phase sample is a 7-bit two’s com-

plement number with a maximum positive value of

0x3f, and a maximum negative value of 0x40. The

terms “positive” and “negative” are defined for a

positive going pulse only. The pulse generation cir-

cuitry automatically inverts the pulse for negative

going pulses. The data stored in the lowest phase

address corresponds to the first phase sample that

will be transmitted in time. The typical voltage step

for each mode of operation is as follows: for E1

Ω mode the typical voltage step is 42 mV/LSB

and for E1 120

Ω mode the typical voltage step is

54 mV/LSB all voltage steps are measured across

the transformer secondary.

The following procedure describes how to enable

and write data into the AWG RAM to produce cus-

tomized pulse shapes to be transmitted for a specif-

ic channel or channels. First, enable the AWG

function for a specific channel or channels by writ-

ing a “1” to the corresponding bits in the AWG En-

able Register (19h) (See Section 14.26 on

page 40). When the corresponding bit or bits in the

AWG Enable Register are set to “0” pre-pro-

grammed pulse shapes are selected for transmis-

sion. Then the desired channel and phase sample

address must be written to the AWG Phase Ad-

dress Register (17h) (See Section 14.24 on

page 39). Once the channel and phase sample ad-

dress have been written, the actual phase sample

data may be entered into the AWG Phase Data

the selected phase sample address selected by the

lower five bits of the AWG Phase Address Regis-

ter (17h) (See Section 14.24 on page 39)).

To change the phase sample address of the selected

channel the user may use either of the following

steps. The user can re-write the phase sample ad-

dress to the AWG Phase Address Register or set the

Auto-Increment bit (Bit 7) in the Global Control

“1” before writing to the AWG Phase Data Regis-

ter. When this bit is set to “1” only the first phase

E1 AWG Example

Figure 13. Arbitrary Waveform UI

CS61880 датащи(PDF) 42 Page - Cirrus Logic

CS61880 датащи(HTML) 42 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

датащи скачать

ссылки URL