DP83256VF-AP NSC [National Semiconductor], DP83256VF-AP Datasheet - Page 35

• Manufacturer Part Number: DP83256VF-AP
• Manufacturer: NSC [National Semiconductor]

4 0 Modes of Operation
4 5 CASCADE MODE
The PLAYER
lel) mode (Figure 4-5) which is used in high bandwidth
point-to-point data transfer applications This is a non-FDDI
mode of operation This is only available on the DP83257
device
Concepts
In the Cascade mode multiple PLAYER
nected together to provide data transfer at multiples of the
FDDI data rate Two cascaded PLAYER
a data rate twice the FDDI data rate three cascaded
PLAYER
data rate etc
Multiple data streams are transmitted in parallel over each
pair of cascaded PLAYER
simultaneously and begin with the JK symbol pair on each
PLAYER
Data is synchronized at the receiver of each PLAYER
vice by the JK symbol pair Upon receiving a JK symbol pair
a PLAYER
indicate the beginning of data reception
The Cascade Ready signals of all PLAYER
open drain ANDed together to create the Cascade Start
signal The Cascade Start signal is used as the input to
indicate that all PLAYER
symbol pair Data is now being received at every PLAYER
device and can be transferred from the cascaded
PLAYER
See Figure 4-6 for more information
Operating Rules
When the PLAYER
the following rules apply
1 Data integrity can be guaranteed if the worst case PMD
2 Even though this is a non-FDDI application the general
transmission skew between parallel media is less than
40 ns For example this amounts to about 785 meters of
fiber optic cable assuming a 1% worst case variance
rules for FDDI frames must be obeyed
a
a
a
a
devices provide a data rate three times the FDDI
device
devices to the host system
a
device asserts the Cascade Ready signal to
device can operate in the Cascade (paral-
a
device is operating in Cascade mode
a
a
devices have received the JK
devices All data streams start
(Continued)
a
a
devices are con-
devices provide
a
devices are
a
de-
a
35
3 Due to the different clock rates the JK symbol pair may
4 The first PLAYER
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 PLAYER
8 To guarantee integrity of the interframe information the
The MACSI device could be used to provide the required
framing and optional FCS support
arrive at different times at each PLAYER
total skew between the fastest and slowest cascaded
PLAYER
must not exceed 80 ns
will present it to the host system and release the Cas-
cade Ready signal The PLAYER
one more JK as it waits for the other PLAYER
to recognize their JK The maximum number of consecu-
tive JKs that can be presented to the host is 2
ed PLAYER
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 approximately within 80 ns of CR release This condi-
tion signifies that not all cascaded PLAYER
have received their respective JK symbol pair with the
allowed skew range
nization Error if the JK symbols are corrupted in the point-
to-point links
user must put at least 8 Idle symbol pairs between
frames The PLAYER
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
(including 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 ending
delimiter
a
a
devices may not report a Cascaded Synchro-
a
devices receiving the JK starting delimiter
devices release their Cascade Ready sig-
a
device to receive a JK symbol pair
a
device will function properly with
a
device will present
a
device The
a
a
devices
devices