MC145572PB Freescale Semiconductor, MC145572PB Datasheet - Page 213

• Manufacturer Part Number: MC145572PB
• Manufacturer: Freescale Semiconductor

Specifications of MC145572PB

• Number Of Line Interfaces: 1
• Control Interface: HDLC
• Lead Free Status / Rohs Status: Not Compliant

MOTOROLA
D.1
D.2
INTRODUCTION
The MC145572 can provide the recovered eye pattern on a received baud–by–baud basis as a serial
digital word once every 12.5 s. Some applications may use this feature for monitoring performance.
This appendix describes a circuit to receive the eye pattern word and convert it to an analog voltage
for display on an oscilloscope.
This appendix includes the schematics and PALASM 2 programmable logic equations to implement
two versions of an eye pattern generator. One design requires manual scaling to the magnitude of
the eye pattern data, while the other design automatically scales to optimize the limited dynamic
range of the DAC. The eye pattern generator takes the data available on the EYEDATA pin and the
clocking from the SYSCLK pin and generates an analog eye pattern for display purposes. Note that
BR14(b0) must be set to a 1 to enable the EYEDATA and SYSCLK outputs.
DISCUSSION
The eye pattern data output from the MC145572 consists of the received 2B1Q quats after the echo
cancelling and DFE functions have been performed on the signal available at the RxP and RxN pins.
The eye pattern data is output in digital form on the EYEDATA pin and is 19 bits long. It is in sign
extended two’s complement form. The eye pattern data generators described here use an 8–bit DAC
(this is sufficient for acceptable display on an oscilloscope) to display the most significant 8 bits of
data including the first sign bit, but not extended sign bits or less significant bits. The 8 bits are shifted
into an 8–bit serial–to–parallel converter and are then latched into an Analog Device’s AD557 DAC.
When the resulting 8–bit window is correctly placed over the 19–bit eye data word, a full scale
(approximately 1 or 2 V peak–to–peak) eye pattern signal is output from the AD557 clearly showing
the 2B1Q quats. See Figure D–1 for an example of the 8–bit window positioned over a portion of
the 19–bit eye data word. In this example, D16 happens to be the sign bit.
Two circuits are shown for decoding the eye pattern data available on the EYEDATA pin. The first
method provides for manual positioning of the 8–bit DAC data window over the 19–bit eye data word.
The manual positioning schematic is shown in Figure D–2. The second method provides for auto-
matic or manual positioning of the 8–bit DAC data window over the 19–bit eye data word. The auto-
matic positioning schematic is shown in Figure D–3. Whenever the manual method is used, the DIP
switches can be changed to correctly position the 8–bit data window. Manual positioning capability
is provided with the automatic positioning circuit, since there may be some conditions in which the
automatic positioner will not stabilize. DIP switches are shown but any convenient binary encoder
may be used.
Freescale Semiconductor, Inc.
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MC145572
EYE PATTERN GENERATOR
D
D–1