Cirrus Logic CS61884 - Manual (Page 26)

CS61884
26 DS485F3
In host mode, TAOS is generated for a particular
channel by asserting the associated bit in the
TAOS
Enable Register (03h) (See Section 14.4 on
page 35).
Since MCLK is the reference clock, it should be of
adequate stability.
9.6 Automatic TAOS
While a given channel is in the LOS condition, if
the corresponding bit in the
Automatic TAOS
Register (0Eh) (See Section 14.15 on page 37) is
set, the device will drive that channel’s TTIP and
TRING with the all ones pattern. This function is
only available in host mode. Refer to
Loss-of-Sig-
nal (LOS) (See Section 10.5 on page 27).
9.7 Driver Failure Monitor
In host mode, the Driver Failure Monitor (DFM)
function monitors the output of each channel and
sets a bit in the
DFM Status Register (05h) (See
Section 14.6 on page 35) if a secondary short cir-
cuit is detected between TTIP and TRING. This
generates an interrupt if the respective bit in the
DFM Interrupt Enable Register (07h) (See Sec-
tion 14.8 on page 36) is also set. Any change in the
DFM Status Register (05h) (See Section 14.6 on
page 35) will result in the corresponding bit in the
DFM Interrupt Status Register (09h) (See Sec-
tion 14.10 on page 36) being set. The interrupt is
cleared by reading the
DFM Interrupt Status
Register (09h) (See Section 14.10 on page 36).
This feature works in all modes of operation E1 75
Ω, E1 120 Ω and T1/J1 100 Ω.
9.8 Driver Short Circuit Protection
The CS61884 provides driver short circuit protec-
tion when current on the secondary exceeds 50 mA
RMS during E1/T1/J1 operation modes.
10. RECEIVER
The CS61884 contains eight identical receivers that
utilize an internal matched impedance technique
that provides for the use of a common set of exter-
nal components for 100
Ω (T1/J1), 120 Ω (E1), and
75
Ω (Ε1) operation (Refer to
Figure 17 on
page 51 ). This feature enables the use of a one
stuffing option for all E1/T1/J1 line impedances.
The appropriate E1/T1/J1 line matching is selected
via the LEN[2:0] and the CBLSEL pins in hard-
ware mode, or via the
Line Length Channel ID
Register (10h) (See Section 14.17 on page 38) and
bits[3:0] of the Line Length Data Register (11h)
(See Section 14.18 on page 39) in host mode. The
receivers can also be configured to use different ex-
ternal resistors to match the line impedance for E1
75
Ω, E1 120Ω or T1/J1 100Ω modes (Refer to
Figure 18 on page 52 ).
The CS61884 receiver provides all of the circuitry
to recover both data and clock from the data signal
input on RTIP and RRING. The matched imped-
ance receiver is capable of recovering signals with
12 dB of attenuation (referenced to 2.37 V or 3.0V
nominal) while providing superior return loss. In
addition, the timing recovery circuit along with the
jitter attenuator provide jitter tolerance that far ex-
ceeds jitter specifications (Refer to
Figure 20 on
page 58 ).
The recovered data and clock is output from the
CS61884 on RPOS/RNEG and RCLK. These pins
output the data in one of three formats: bipolar, un-
ipolar, or RZ. The CLKE pin is used to configure
RPOS/RNEG, so that data is valid on either the ris-
ing or falling edge of RCLK.
10.1 Bipolar Output Mode
Bipolar mode provides a transparent clock/data re-
covery for applications in which the line decoding
is performed by an external framing device. The re-
covered clock and data are output on RCLK,
RNEG/BPV, and RPOS/RDATA.
10.2 Unipolar Output Mode
In unipolar mode, the CS61884 decodes the recov-
ered data with either B8ZS, HDB3 or AMI line de-
coding. The decoded data is output on the