ACS102A Semtech Corporation, ACS102A Datasheet - Page 4

• Manufacturer Part Number: ACS102A
• Description: Acs102a Fiber Modem
• Manufacturer: Semtech Corporation

Table 1. TxD Data-Rate Selection
Table 1. shows the maximum TxD data rate, which includes a 10%
tolerance margin, when using various frequency crystals, other
sample-clock frequencies may be generated by using the
appropriate value XTAL in combination with the divide constant
selected by DR(1:3) namely 15,20,40,80 or 160.
The advantage of using a slower crystal and a lower sample clock
is the reduced power consumption of the device.
Three additional low frequency data channels are provided on the
ACS102A which are often used for the RS-232 handshake signals.
The RS-232 handshake signals comprise the set RTS, CTS, DTR
and DSR. These are treated as pass through data channels rather
than using local handshaking. Hence the status of inputs RTS and
DTR appear at the far-end outputs CTS and DSR respectively. An
extra data channel has also been provided, which may be used for
sending the RS232 Ring Indicator signal, for example. The input
and output lines are RII and RIO respectively.
The transmission method employed on the ACS102 has been
designed to give low skew (1 - 2 data-bits) on the main RTS, CTS,
DTR and DSR handshake signals relative to the main TxD/RxD
data channel, while maintaining low power consumption.
The handshake signals are updated by two stimuli:
i.
ii.
The maximum bandwidth for the handshake signals may be
programmed using pins HD(1:2) in accordance with the Table 2.
Table 2. Handshake signal bandwidth allocation
* When HD2 = HD1 = 0 super-compress mode is selected. See
section headed Super-Compress mode.
Handshake data rates which exceed the allocated bandwidth will
be delayed, and consequently result in additional skew between
handshake signals and data.
The HD pins enable the user to allocate a maximum bandwidth to
the handshake signals and thus limit the power consumption of the
device. The power consumption is, however, dependent on the
actual bandwidth used and not the bandwidth selected.
example; if the handshake signals were toggled at 1kHz the power
consumption would be the same for an allocated bandwidth of
2.5kHz as it would for an allocation of 10kHz. See section headed
Current and Power Consumption for more details.
This mode is selected when HD2 = HD1 = 0. Super-compress
mode performs a second stage of data compression, thus further
reducing the power consumption of the modem. Normally, data is
compressed in a manner which is independent of the data type. In
super-compress mode, an additional stage of compression further
reduces the data by a factor of 1 to 3 depending on the data itself.
Example: The super-compress stage will compress DC data by an
additional Compression Factor (CF) of 3, whilst data close to the
RS-232 Handshake Signals / Low Frequency Data Channels
Super-Compress mode
DR3
HD2
0
1
1
1
1
1
1
0
0
1
1
an internal interval timer at a frequency proportional to the
XTAL; at 10.0MHz this is approximately 1.6ms.
changes detected on RTS and DTR.
Advanced Communications
DR2
1
0
0
1
1
1
1
HD1
0*
1
0
1
DR1
1
0
1
0
1
1
1
600
10
5
2.5
Frequency
10MHz
10MHz
10MHz
10MHz
10MHz
20MHz
27MHz
Clock
XTAL
Sampling
Hz
kHz
kHz
kHz
XTAL/160
XTAL/80
XTAL/40
XTAL/20
XTAL/15
XTAL/15
XTAL/15
Sample
Clock
10 ms.
1 - 2 data bits
1 - 2 data bits
1 - 2 data bits
w.r.t. RxD
Skew
120kbps
162kbps
5.6kbps
11kbps
22kbps
45kbps
60kbps
Data Rate
Max TxD
For
4
maximum frequency will not be compressed beyond the standard
CF of 1.
Super-compress mode provides benefits where the user is
interested in low average power consumption (e.g. battery life)
rather than peak power. If the intended system is idle for most of
the time with periodic bursts of activity, the additional data
compression afforded will approach a CF of 3.
To achieve low power consumption the ACS102A is active for a
small percentage of the frame (machine-cycle) known as the
'transmit' window and the 'receive' window, collectively these
windows are known as the 'active time'. Outside the 'active time'
the device is largely dormant accept for the maintenance of the
oscillator and basic 'house-keeping' functions.
Communicating modems attain a stable state known as 'locked',
where the 'transmit' window of one modem coincides with the
'receive' window of the other, allowing for the delay through the
optical link.
automatically during operation, to compensate for differences in
XTAL frequencies which cause loss of synchronisation.
The ACS102A locking algorithm is statistical, and consequently
the locking time will differ on each attempt to lock.
The diagnostic and operational modes, shown in Table 3, are
selected using the DM pins.
Table 3. Diagnostic and operational modes
Local Loopback
In local loopback mode TxD data is looped back inside the near-end
modem and appears at its own RxD output. RTS, DTR and RII are
also looped back appearing at their own CTS, DSR and RIO outputs
respectively.
synchronisation between the modems is maintained.
In local loopback mode data received from the far-end device is
ignored, except to maintain lock. If concurrent requests occur for
local and remote loopback, local loopback is selected.
The local loopback diagnostic mode is used to test data flow up to,
and back from, the local ACS102A and does not test the integrity of
the link itself, i.e. local loopback operates independently of
synchronisation with a second modem.
Remote Loopback
In remote loopback mode, the near-end modem sends a request to
the far-end modem to loopback its received data, thus returning the
data so that it appears at the RxD of the initiating modem. RTS,
DTR and RII follows the same path, returning data back to CTS,
DSR and RIO respectively of the initiating modem.
appears at the far-end modem outputs RxD, CTS, DSR and RIO. In
the process both modems are exercised completely, as well as the
LED/PINs and the fiber optic link. The remote loopback test is
normally used to check the integrity of the entire link from the near-
end (initiating) modem. Whilst a device is responding to a request
for remote loopback from the initiating modem (far-end), requests to
initiate remote loopback will be ignored.
Drift lock
Communicating modems attain a stable state where the 'transmit'
window of one modem coincides with the 'receive' window of the
other, allowing for delay through the optical link. Adjustments to
machine cycles are made automatically during operation to
compensate for differences in XTAL frequencies which would
otherwise cause loss of synchronisation.
Locking
Diagnostic and Locking Modes
DM3
0
0
0
1
1
1
DM2
0
0
1
0
1
1
The data is also sent to the far-end modem and
Adjustments to machine cycles are made
DM1
0
1
0
1
0
1
Mode
Full-duplex
Full-duplex
Full-duplex
Local loopback
Remote loopback
Full-duplex
ACS102A Data Sheet
Lock
Drift
Active
Memory
Random
Random
Random
Data also