Cirrus Logic CS61884 - Manual (Page 25)

CS61884
DS485F3 25
The CS61884 also allows the user to customize the
transmit pulse shapes to compensate for non-stan-
dard cables, transformers, or protection circuitry.
For further information on the AWG Refer to
Ar-
bitrary Waveform Generator (See Section 15 on
page 43).
For more information on the host mode registers,
refer to
Register Descriptions (See Section 14 on
page 35).
9.1 Bipolar Mode
Bipolar mode provides transparent operation for
applications in which the line coding function is
performed by an external framing device. In this
mode, the falling edge of TCLK samples NRZ data
on TPOS/TNEG for transmission on TTIP/TRING.
9.2 Unipolar Mode
In unipolar mode, the CS61884 is configured such
that transmit data is encoded using B8ZS, HDB3,
or AMI line codes. This mode is activated by hold-
ing TNEG/UBS “High” for more than 16 TCLK
cycles. Transmit data is input to the part via the
TPOS/TDATA pin on the falling edge of TCLK.
When operating the part in hardware mode, the
CODEN pin is used to select between B8ZS/HDB3
or AMI encoding. During host mode operation, the
line coding is selected via the
Global Control Reg-
ister (0Fh) (See Section 14.16 on page 38).
NOTE: The encoders/decoders are selected for all
eight channels in both hardware and host
mode.
9.3 RZ Mode
In RZ mode, the internal pulse shape circuitry is
bypassed and RZ data driven into TPOS/TNEG is
transmitted on TTIP/TRING. In this mode, the
pulse width of the transmitter output is determined
by the width of the RZ signal input to
TPOS/TNEG. This mode is entered when MCLK
does not exist and TCLK is held “High” for at least
12
μsec.
9.4 Transmitter Powerdown / High-Z
The transmitters can be forced into a high imped-
ance, low power state by holding TCLK of the ap-
propriate channel low for at least 12
μs or 140
MCLK cycles. In hardware and host mode, the
TXOE pin forces all eight transmitters into a high
impedance state within 1
μs.
In host mode, each transmitter is individually con-
trollable using the
Output Disable Register (12h)
(See Section 14.19 on page 39). The TXOE pin can
be used in host mode, but does not effect the con-
tents of the Output Enable Register. This feature is
useful in applications that require redundancy.
9.5 Transmit All Ones (TAOS)
When TAOS is activated, continuous ones are
transmitted on TTIP/TRING using MCLK as the
transmit timing reference. In this mode, the TPOS
and TNEG inputs are ignored.
In hardware mode, TAOS is activated by pulling
TCLK “High” for more than 16 MCLK cycles.
Table 5. Hardware Mode Line Length Configuration Selection
LEN[2:0] Transmit Pulse Configuration Line Z Operation
000 E1 3.0V / E1 2.37V 120
Ω / 75Ω
E1
001 DS1, Option A (undershoot) 100
Ω
T1/J1
010 DS1, Option A (0 dB) 100 Ω T1/J1
011 DSX-1: 0-133 ft. (0.6dB) 100
Ω
T1/J1
100 DSX-1: 133-266 ft. (1.2dB) 100
Ω
T1/J1
101 DSX-1: 266-399 ft. (1.8dB) 100
Ω
T1/J1
110 DSX-1: 399-533 ft. (2.4dB) 100 Ω T1/J1
111 DSX-1: 533-655 ft. (3.0dB) 100
Ω
T1/J1