HDMP-1012 Datasheet, PDF (24/42 Pages) Agilent(Hewlett-Packard) – 4Low Cost Gigabit Rate Transmit/Receive Chip Set

Appendix I: Additional
Internal Architecture
Information
Line Code Description
The HDMP-1012/1014 line code
is Conditional Invert Master
Transition (CIMT), illustrated in
Figure 11. The CIMT line uses
three types of frames: data
frames, control frames, and fill
frames. Fill frames are internally
generated by the Tx chip for use
during link start up and when
there is no input from the user.
Each frame consists of a Data
Field (D-Field) followed by a
Coding Field (C-Field). The D-
Field can be either 16-bits or 20-
bits wide, depending on link
configuration. The C-Field has a
master transition which serves as
a fixed timing reference for the
receivers clock recovery circuit.
Users can send arbitrary data
carried by Data or Control
Frames. The dc balance of the
line code is automatically
enforced by the Tx. Fill frames
have a single rising edge at the
master transition which is used
for clock recovery and frame
synchronization at the receiver.
Detailed coding schemes are
described in the following
subsections. All the tables given
in this section show data bits in
the same configuration as a scope
display. In other words, the
leftmost bit in each table is the
first bit to be transmitted in time,
while the rightmost bit is the last
bit to be transmitted.
SERIAL
DATA
DATA FIELD
16/20 BITS
FILL
FRAME
FRAME K
Figure 11. HDMP-1012/1014 (Tx/Rx Pair) Line Code.
CODING FIELD
4 BITS
MASTER
TRANSITION
FRAME K+1
Data Frame Codes
When not in FLAGSEL mode, the
FLAG bit is not user controllable
and is alternately sent as 0 and 1
by the Tx chip during data frames
to provide enhanced error
detection. Control and Fill frames
do not cause toggling between
even and odd frames to occur
(The FLAG bit is not available
during control frames). The
receiver performs a differential
detection to make sure that every
data frame received is the
opposite pattern from the
previous frame. If a break in the
strict alternation is observed, a
frame error is flagged by
asserting the Rx ERROR output.
This pattern detection makes it
impossible for a static input data
pattern to generate an
undetectable false lock point in
the transmitted data stream. The
detection also reduces the
probability that the loop could
lock onto random data at a point
away from the true master
transition for any significant time
before it would be detected as a
false lock. This mode can detect
all single-bit errors in the C-field
(non-data bit fields) of the frame.
When the chip is in FLAGSEL
mode, the extra FLAG bit is freely
user definable as an extra data
bit. This provides a 17th bit in 16
bit mode, and a 21st bit in 20 bit
mode. The probability of
undetected false lock is higher,
but the users (e.g., SCI-FI) that
need the extra bit can detect false
lock at a higher level of the
network protocol with clock
recovery circuits, etc. If the
higher level protocols consistently
receive wrong data, they can
initiate a link restart by resetting
the Rx state machine.
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