dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 18

• Manufacturer Part Number: dp83251
• Description: Player Device Fddi Physical Layer Controller
• Manufacturer: National Semiconductor Corporation

4 0 Modes of Operation
4 4 CASCADE MODE
The PLAYER device can operate in the Cascade (parallel)
mode Figure 4-4
to-point data transfer applications This is a non-FDDI mode
of operation
CONCEPTS
In the Cascade mode multiple PLAYER devices are con-
nected together to provide data transfer at multiples of the
FDDI data rate Two cascaded PLAYER devices provide a
data rate twice the FDDI data rate three cascaded PLAYER
devices provide a data rate three times the FDDI data rate
etc
Multiple data streams are transmitted in parallel over each
pair of cascaded PLAYER devices All data streams start
simultaneously and begin with the JK symbol pair on each
PLAYER device
Data is synchronized at the receiver of each PLAYER de-
vice by the JK symbol pair Upon receiving a JK symbol pair
a PLAYER device asserts the Cascade Ready signal to indi-
cate the beginning of data reception
The Cascade Ready signals of all PLAYER devices are
open drain ANDed together to create the Cascade Start
signal The Cascade Start signal is used as the input to
indicate that all PLAYER devices have received the JK sym-
bol pair Data is now being received at every PLAYER de-
vice and can be transferred from the cascaded PLAYER
devices to the host system
See Figure 4-5 for more information
OPERATING RULES
When the PLAYER device is operating in Cascade mode
the following rules apply
1 Data integrity can be guaranteed if the worst case fiber
2 Even though this is a non-FDDI application the general
optic transmission skew between parallel fiber cables is
less than 40 ns This amounts to about 785 meters of
fiber assuming a 1% worst case variance
rules for FDDI frames must be obeyed
which is used in high bandwidth point-
(Continued)
18
3 Due to the different clock rates the JK symbol pair may
4 The first PLAYER device to receive a JK symbol pair will
5 The Cascade Start signal is set to 1 when all the cascad-
6 Bit 4 (CSE) of the Receive Condition Register B (RCRB)
7 If the JK symbols are corrupted in the point-to-point links
8 To guarantee integrity of the interframe information the
The BMAC device could be used to provide required fram-
ing and optical FCS support


arrive at different times at each PLAYER device The total
skew between the fastest and slowest cascaded PLAY-
ER devices receiving the JK starting delimiter must not
exceed 80 ns
present it to the host system and assert the Cascade
Ready signal The PLAYER device will present one more
JK as it waits for the other PLAYER devices to recognize
their JK The maximum number of consecutive JKs that
can be presented to the host is 2
ed PLAYER devices release their Cascade Ready sig-
nals
is set to 1 if the Cascade Start signal (CS) is not set
before the second falling edge of clock signal LBC from
when Cascade Ready (CR) was released CS has to be
set within approximately 80 ns of CR release This condi-
tion signifies that not all cascaded PLAYERs have re-
ceived their respective JK symbol pair within the allowed
skew range
some PLAYER devices may not report a Cascaded Syn-
chronization Error
user must put at least 8 Idle symbol pairs between
frames The PLAYER device will function properly with
only 4 Idle symbol pairs however the interframe symbols
may be corrupted with random non-JK symbols
Data frames must be a minimum of three bytes long (in-
cluding the JK symbol pair) Smaller frames will cause
Elasticity Buffer errors
Data frames must have a maximum size of 4500 bytes
with a JK starting delimiter and a (T or R or S)x or x(T or
R or S) ending delimiter byte