AD9639 Analog Devices, Inc., AD9639 Datasheet - Page 24

• Manufacturer Part Number: AD9639
• Description: Quad, 12-bit, 170 Msps/210 Msps Serial Output 1.8 V Adc
• Manufacturer: Analog Devices, Inc.

AD9639
Continuous Synchronization
Continuous synchronization is part of the JESD204 specification.
The 12-bit word requires two octets to transmit all the data. The
two octets (MSB and LSB) are called a frame. When scrambling
is disabled and the LSB octets of two consecutive frames are the
same, the second LSB octet is replaced by a K28.7 comma symbol.
The receiver is responsible for replacing the K28.7 comma
symbol with the LSB octet of the previous frame.
Table 9. Variables and Functions in Data Dependent Frame Synchronization
Variable
N
/K28.7/
OCOUNTER
PREVIOUS_POSITION
/REPLACE_K28.7/
/RESET_OCTET_COUNTER/
/VALID/
Description
Number of octets in frame (octet indexing starts from 0).
Asserted when the current symbol corresponds to the K28.7 control character.
Counter used to mark the position of the current octet in the frame.
Variable that stores the position in the frame of a K28.7 symbol.
Replace K28.7 at the decoder output as follows. When scrambling is disabled, replace K28.7 with the LSB
octet that was decoded at the same position in the previous frame; when scrambling is enabled, replace
K28.7 at the decoder output with D28.7.
Reset octet counter to 0 at reception of next octet.
Asserted by receiver to indicate that the current symbol is a valid symbol given the current running disparity.
Figure 56. Pseudocode for Data Dependent Frame Synchronization in Receiver
IF /K28.7/
END IF;
/REPLACE_K28.7/
IF (OCOUNTER == PREVIOUS_POSITION) AND /VALID/
END IF;
IF /VALID/ | (OCOUNTER == N-1)
END IF;
/RESET_OCTET_COUNTER/
PREVIOUS_POSITION = OCOUNTER
Rev. 0 | Page 24 of 36
When scrambling is enabled, any D28.7 symbols found in the
LSB octet of a frame are replaced with K28.7 comma symbols.
The receiver is responsible for replacing the K28.7 comma
symbols with D28.7 symbols when in this mode.
By looking for K28.7 symbols, the receiver can ensure that it is
still synchronized to the frame boundary.