ACS406CS Semtech Corporation, ACS406CS Datasheet - Page 7

• Manufacturer Part Number: ACS406CS
• Description: Two-chip Fiber Optic Modem Ics / ACS4060 100-pin Tqfp, ACS9010 44-pin TQFP
• Manufacturer: Semtech Corporation

If one of the 8-channel modes is selected by the
DR(5:1) inputs, then the ACS406CS must be
configured to expect Non-Return-to-Zero (NRZ)
transmission data using the POL1/2 settings. The
otherwise redundant TNEG and RNEG pins are then
available to carry 4 additional data channels. The
mapping of transmission pins for 8-channel NRZ
operation can be seen in Table 6.
There are three transmission modes available on
the ACS406CS selected by the DR(5:1) pins, these
are TX1, TX2, TX4 and HT modes.
In TX1 mode all of the data channels (TPN/RPN)
are related to the clocks TCLK1/RCLK1.
In TX2 mode there are two system clocks, half the
signals are aligned to the clock TCLK1/RCLK1 and
the remaining half are aligned to the clock TCLK2/
RCLK2.
For dual channel operation, channel 1 is aligned to
clock TCLK1/RCLK1 and channel 2 is aligned to clock
TCLK2/RCLK2.
For four channel operation, channels 1-2 are aligned
to clock TCLK1/RCLK1 and channels 3-4 are aligned
to clock TCLK2/RCLK2.
For eight channel operation, channels 1-4 are aligned
to clock TCLK1/RCLK1 and channels 5-8 are aligned
to clock TCLK2/RCLK2.
8-Channel Operation
TX1 mode
TX2 mode
Transmission Modes (TMode)
Channel Nos.
Channel Nos.
1
2
3
4
5
6
7
8
1
2
3
4
TPOS1/TNEG1
TPOS2/TNEG2
TPOS3/TNEG3
TPOS4/TNEG4
Input
TPOS1
TNEG1
TPOS2
TNEG2
TPOS3
TNEG3
TPOS4
TNEG4
Input
RPOS1/RNEG1
RPOS2/RNEG2
RPOS3/RNEG3
RPOS4/RNEG4
Table 5
Output
Output
RPOS1
RNEG1
RPOS2
RNEG2
RPOS3
RNEG3
RPOS4
RNEG4
Table 6
7
In TX4 mode there are four system clocks. TX4 mode
operates only in conjunction with 4 channel operation.
Channel 1 is aligned to TCLK1/RCLK1, channel 2
with TCLK2/RCLK2, channel 3 with TCLK3/RCLK3
and channel 4 with TCLK4/RCLK4.
Acapella recognises that a large number of designers
using the ACS406CS modem will be employing the
device for single channel T1 or single channel E1
operation. In such cases, the available bandwidth far
exceeds the bandwidth required. To exploit this
otherwise redundant bandwidth, the ACS406CS
incorporates a High Tolerant (HT) transmission mode.
In HT mode, by virtue of on-chip error-correction,
the device is extremely tolerant to data errors.
All modes in the ACS406CS generate regular unique
Synchronisation Words (SWs) in order to re-enforce
8B10B word boundary synchronisation. This prevents
single bit-errors causing an avalanche of errors due
to word boundary slippage, often referred to as "error
extension". In HT mode, SWs are interleaved with
the data-words such that alternate words are SWs,
ensuring that the effect of 8B10B word boundary
errors will not propagate beyond one received data
word.
In HT mode the single data channel is aligned to the
TCLK1/RCLK1 clock.
Some customers will require a modem capable of
supporting a longer distance than the standard 25km.
To support this Acapella have implemented a 50km
mode for a single E1 or T1 channel. This is achieved
with an XTAL of value half of that used for the
standard E1 or T1 for 25km modes in combination
with the appropriate configuration of the DR(5:1) pins.
NOTE: The designer should be aware that the use
of lower value crystal will proportionally increase the
end-to-end data delay through the system in
accordance with the formula found in section headed,
Data Delay (Latency). Therefore, for the 50km mode
the latency will double compared to the standard
25km modes.
A set of example configurations follow:
In order to select one E2 operation then set DR5 = DR4
= DR3 = DR2 = DR1 = 1, together with a crystal of
33.792MHz as shown in the Table 7.
TX4 mode
HT mode
50km long haul mode
Example Data Rate Selection
E2 Selection
ACS406CS Issue 1.6 January 1999.