ACS101A Semtech Corporation, ACS101A Datasheet - Page 2

• Manufacturer Part Number: ACS101A
• Description: Acapella Optical Modem ic
• Manufacturer: Semtech Corporation

Modes for Asynchronous Data :
Modes for Synchronous Data :
Standard' mode of operation is up to 2.5km, 'double' mode is up to
5km and 'short' is up to 1.25km. Other non-standard data-rates
may be generated by using different crystal frequencies as long as
the 5 - 19MHz crystal range is observed.
Acapella Optical Modem IC
The 3B4B encoding method is used for communication between
ACS101A, thus ensuring that there is no DC component in the
signal. The encoding and decoding is transparent to the user.
The TxD input data of the transmitting modem is compressed,
filtered, and 3B4B encoded.
encoding ensures easy extraction of the bit-clock. The received
data is filtered, decoded, then stored in an output memory. The
memory provides time expansion, de-jittering and frequency
compensation. Finally, the data is filtered again to improve BER
then directed to the RxD output pin.
The transmit current to the LED can be defined by the Transmit
Current pin (TRC).
(~100mA) when TRC is unconnected. The current is set to the
minimum value (~10mA) when TRC is connected directly to
ground. To obtain current values between minimum and maximum
TRC is connected to ground through a resistor. The resistor value
R is given by:
LED current drive (mA) =
DR4 DR3 DR2 DR1
DR4 DR3 DR2 DR1
ACS101A Issue 1.2 October 1999.
Inter-IC Encoding Technique
Transmitter and Receiver Functions
Transmit Current
Data-rate Selection DR1 to DR4
1
0
1
1
0
0
0
0
0
1
1
1
1
1
1
0
0
0
1
1
1
0
0
0
1
1
0
0
0
0
1
1
1
1
0
0
1
1
1
0
1
1
0
1
0
0
1
1
0
0
1
0
0
0
0
0
0
1
0
1
0
1
0
1
0
1
0
1
1
1
0
0
The current is set to the maximum value
XTAL freq
XTAL freq
18.432
18.432
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
9.216
(MHz)
(MHz)
Synchronous or Asynchronous Single Fiber Modem
In the receiving modem, 3B4B
Data-rate
Data-rate
DC - 19.2
DC - 38.4
DC - 76.8
(kbps)
(kbps)
192.0
256.0
512.0
100 * (110+R)
19.2
38.4
48.0
64.0
19.2
38.4
48.0
56.0
64.0
9.6
2.4
9.6
(1100+R)
Distance
Distance
Short
Standard
Standard
Standard
Standard
Short
Double
Standard
Double
Double
Double
Double
Double
Standard
Standard
Standard
Standard
Standard
2
RSS Low - Data Transmission Mode.
RSS High - Modem Handshake Mode.
DSR (Data Set Ready) DCE
DTR (Data Terminal Ready) DTE
RTS (Request to Send) DTE
CTS (Clear to Send) DCE
DCDB (Data Carrier Detect) DCE
For data-rates of 9.6, 19.2, 33.4, 48 and 64kbps the data-rate
selection pins DR1-DR3 are common to standard and double
modes of operation, with DR4 selecting the distance mode.
RSS.
RTS, CTS, DTR and DSR signals may be used in either of two
modes, depending on the RSS setting:
RSS = Low; data transmission mode
RSS = High; modem handshake mode
In data transmission mode the inputs RTS and DTR are sampled
continuously at (crystal freq.) / 1536, 6.0kHz with a crystal of
9.216MHz. The outputs appear at CTS and DSR respectively.
In modem handshake mode the control signals are used as
conventional handshake signals between the DTE (terminal) and
the DCE (modem):
The DCE is powered up and asserts a Low (active level) on DSR.
The DTE is informed that it is connected to a “live” DCE.
The DTE is powered-up and asserts a Low (active level) on DTR.
The DCE is informed that it is connected to a “live” DTE. If DTR is
set High, the DCE responds by asserting DCDB High.
The DTE recognises that synchronisation has been achieved
(DCDB active) and asserts a Low (active level) on RTS. This
constitutes a request by the DTE to send data to the far-end
modem.
The DCE recognises the active RTS signal and responds by
asserting a Low (active level) on CTS. If RTS is set High the DCE
responds by bringing CTS High.
When synchronisation is achieved between DCEs the DCDB
signal is set Low (active level). If synchronisation is lost the DCE
sets DCDB and CTS High.
A crystal may be connected between the pins XLI and XLO.
Alternatively, XLI may be driven directly by an external clock. The
operational frequency range is 5MHz to 19MHz, though
communicating devices must be driven at the same nominal
frequency with a tolerance of 100ppm. In synchronous mode the
frequency should be 9.216MHz, resulting in the standard range of
synchronous communication frequencies selected by DR1-DR4.
Crystal Clock
Modem Control Signals
DTE.
DTE.
DCE.
DCE.
ACS101A
DTE.