ACS405CS Semtech Corporation, ACS405CS Datasheet - Page 2

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

The ACS405CS comprises a chip-set of two highly
integrated devices, the ACS9010 and ACS4050. The
ACS9010 is an analogue device and the ACS4050
is predominately a digital device.
The ACS9010 contains the Laser/LED driver as well
as the PIN receiver circuitry. Since the device does
not transmit and receive concurrently (ping-pong),
there is no risk of noise generated by the transmitter
interfering with the sensitive receive circuitry.
The ACS4050 comprises the logic necessary to time
compress and decompress the data, plus all the
logic associated with window synchronisation and
locking.
For the purpose of this specification the chip-set
will be referred to as the ACS405CS and the
individual devices as the ACS9010 or ACS4050.
The inter-IC coding between communication modems
is 8B10B. Whilst transparent to the user, 8B10B
encoding ensures that there is no DC component in
the signal, and provides frequent data transitions,
factors which ease the task of data recovery and
clock extraction.
The coding rules are continuously checked to ensure
the integrity of the link, and errors are indicated on
the ERRL and ERRC pins ( see section headed
ERRC and ERRL - Error Detection ).
Data presented at the near-end TPOS/TNEG is time-
compressed, encoded in the 8B10B format and
transmitted over the link in a high frequency burst.
The optical interface is then configured as a receiver
ready to accept data from the far-end. The received
data is decoded, time decompressed and de-jittered
and then presented to the RPOS/RNEG data output
pins.
The Power-On Reset (PORB) pin resets the device
if forced low for 2ms or more. In normal operation
PORB should be held High. It is recommended that
PORB is connected to VD+ via a 100K
and to GND via a 100nF capacitor.
PORB has a special function when used in
conjunction with memory lock (see section headed
Diagnostic Modes ).
The system clock on the ACS405CS may be derived
Acapella Optical Modem IC
Inter-Modem Coding
The Transmit and Receiver Functions
PORB
System Clock
resistor
2
from an external source or generated locally using
the on-chip crystal oscillator. The oscillator (XTO/I)
requires the use of a fundamental parallel resonance
crystal with appropriate padding capacitors. The
input pin, SCEXT should be connected to GND. The
crystal specification should be:
Calibration tolerance: +/- 20ppm @ 25ºC
Temp. tolerance:
Temperature range:
Load condition:
Padding capacitor:
If it is required to drive the device with an externally
generated system clock source, then the clock
source should be connected to input pin ECLK with
SCEXT connected to VD+. It is often more
convenient to drive boards containing multi
ACS405CS chip-sets from a single system clock
source.
The system clock frequency is determined by the
choice of data rates and is tabulated in section
headed, Data Rate Selection. For example, for E2
operation, the appropriate frequency is 33.792MHz
and for T2 operation, 31.560MHz.
The system clock defines the burst frequency at
which data is transmitted over the optical link via
the optical interface. The receive circuitry within the
ACS4050 recovers the clock from the received data
at the Rxdat inputs and produces a clock that is
synchronised to the incoming data stream. The
system clock must have a maximum tolerance of +/-
50ppm over the desired temperature range.
The ACS405CS has four optical operational modes
controlled by the pins LASER, LASRX and PINRX
on the ACS9010 device. All of the duplex modes in
Table 1 may be converted to dual fiber operation
simply by interfacing to separate transmitting and
receiving devices.
Mode 1 - Laser Duplex using 4-pin Laser
In mode 1, the device is configured for use with a
Laser duplex device containing a 4-pin laser. The
diagram below shows the connections to the
ACS9010 device. The operational control pins found
on the ACS9010 are configured as follows:
Optical Operational Modes
Mode
1
2
3
4
18-22pF (tune for desired tolerance)
parallel load 15pF
+/- 20ppm @ -40 to +85ºC
-40 to +85ºC
Optical Device
Laser Duplex using 4-pin Laser.
Laser Duplex using 3-pin Laser.
LED Duplex.
LED (ping-pong).
ACS405CS
ACS405CS Issue 4.3 June 1999.
Table 1