ACS405CS Semtech Corporation, ACS405CS Datasheet - Page 13

• Manufacturer Part Number: ACS405CS
• Description: Acapella Optical Modem ic
• Manufacturer: Semtech Corporation

The power coupled to the cable is a function of the
efficiency of the Laser/LED, the current applied to
the Laser/LED and the type of the fiber optic cable
employed.
The ACS4050 may be used without the ACS9010
device with custom external circuitry for non-fiber
applications. Please check with Acapella for details.
There are two conditions that will make LOSS go to
logic 1:
i) Loss of synchronisation - ping-pong windows
incorrectly aligned i.e DCD = 0.
ii) 64 received symbols break the 8B10B encoding
rules in a sequence of 256 symbols.
In order to return LOSS to the logic state 0 the
following criteria must be met.
i) The devices must be synchronised - ping-pong
windows correctly aligned i.e DCD = 1.
ii) There are no received symbols in a sequence of
256 symbols which break the 8B10B coding rules.
Although the ACS405CS is a full-duplex modem, at
the fiber level the device operates in a half-duplex
manner.
bidirectional transmission by alternating the direction
of data flow. This means that data must be stored
until the link is configured in the appropriate
direction. Storage inevitably leads to delay or
latency. Acapella has designed the ACS405CS to
minimise latency by very rapidly switching direction
at the fiber level, minimising the need to store data.
Digital Mode
LOSS ( Loss Of Synchronisation)
Data Delay (Latency)
Typically, half-duplex systems allow
13
The latency through the system applies to the main
data TPOS/TNEG channels and the support
channels TmD/RmD and is a function of the XTAL
frequency. For a given implementation, the latency
has three components:
1) A Constant Delay (CD) set by the machine cycle
and system clock at a frequency of 32.768MHz then
CD = 0.7ms.
2) A Transmission Rate Delay (TRD) which is equal
to 125 bit periods worst case (de-jittering buffer and
internal registers)
3) Fiber length Dependent Delay (FDD) which is
equal to 2 * (fiber delay)
The Latency formula is
(0.7 * 10
* fiber delay),
Example Latency calculation
Latency calculation:
Fiber length
XTAL
DR mode
Latency = ((0.7 * 10
10
-9
) + ( 2* 50 * 10
-3
* 32.768 * 10
where the
= 10km ( ~ 50us)
= 33.792MHz
= 4 * 2.048Mbps ( transmit bit period = 488ns)
-3
-6
)) = 0.84ms
* 32.768 * 10
-6
/XTAL) + (125 * transmit bit period) + (2
fiber delay is typically 5us per km.
:
-6
/33.792 * 10
ACS405CS Issue 4.3 June 1999.
-6
) + (125 * 488*