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PA-8T-232 Synchronous Serial Port Adapter Installation and Configuration
OL-3562-03
Chapter 5 Configuring the PA-8T-232 Interfaces
Configuring the EIA/TIA-232 Interfaces
Inverting the Clock Signal
Systems that use long cables or cables that are not transmitting the TxC (clock) signal might experience
high error rates when operating at the higher transmission speeds. If a PA-8T-232 DCE port is reporting
a high number of error packets, a phase shift might be the problem: inverting the clock might correct this
phase shift.
When the EIA/TIA-232 interface is a DTE, the invert-txc command inverts the TxC signal the DTE
receives from the remote DCE. When the EIA/TIA-232 interface is a DCE, the invert-txc command
inverts the clock signal to the remote DTE port. Use the no invert-txc command to change the clock
signal back to its original phase.
Inverting the Data Signal
If you use an EIA/TIA-232 interface on the PA-8T-232 port adapter to drive a dedicated T1 line that does
not have B8ZS encoding—a method to avoid 15 zeros—you must invert the data stream (both TXD and
RXD) either in the connecting CSU/DSU or on the interface. To invert the data stream coming out of the
PA-8T-232, use the invert data command. By inverting the HDLC data stream, the HDLC zero insertion
algorithm becomes a ones insertion algorithm that satisfies the T1 requirements.
Note
Invert data only on the PA-8T-232 interface or on the CSU/DSU; inverting both cancel out both data
inversions.
Configuring NRZI Format
summarizes NRZI format commands. For more information, see the remainder of this section.
All EIA/TIA-232 interfaces on the PA-8T-232 support non return-to-zero (NRZ) and non return-to-zero
inverted (NRZI) formats. Both formats use two different voltage levels for transmission. NRZ signals
maintain constant voltage levels with no signal transitions—no return to a zero voltage level—during a
Table 5-5
NRZI Format Commands
Purpose
Command
Example
Further Information
Enable NRZI
encoding.
nrzi-encoding
[mark]
1
1.
Mark is an optional argument. When mark is used, it means there is no signal transition; there is data (a mark) at the beginning of a bit interval. When
mark is not used, it means there is a signal transition; there is no data (a space) at the beginning of a bit interval.
The example is for a serial interface with NRZI
mark encoding specified:
Router(config)# interface serial 3/0
Router(config-if)# nrzi-encoding mark
The example is for a serial interface with NRZI
space encoding specified:
Router(config)# interface serial 3/0
Router(config-if)# nrzi-encoding
Disable NRZI
encoding.
no nrzi-encoding
The example disables NRZI encoding on a serial
interface:
Router(config)# interface serial 3/0
Router(config-if)# no nrzi-encoding
