clock rate
To configure the clock rate for the hardware connections on serial interfaces such as network interface modules (NIMs) and interface processors to an acceptable bit rate, use the clockrate command in interface configuration mode. To remove the clock rate if you change the interface from a DCE to a DTE device, use the no form of this command. Using the no form of this command on a DCE interface sets the clock rate to the hardware-dependent default value.
clock rate bps
no clock rate
Syntax Description
bps |
Desired clock rate, in bits per second: 1200 , 2400 , 4800 , 960 0, 19200 , 38400 , 56000 , 64000 , 72000 , 125000 , 148000 , 250000 , 500000 , 800000 , 1000000 , 1300000 , 2000000 , 4000000 , or 8000000 For the synchronous serial port adapters (PA-8T-V35, PA-8T-X21, PA-8T-232, and PA-4T+), a nonstandard clock rate can be used. You can enter any value from 300 to 8000000 bps. The clock rate you enter is rounded (adjusted), if necessary, to the nearest value that your hardware can support except for the following standard rates: 1200 , 2400 , 4800 , 960 0, 14400 , 19200 , 28800 , 38400 , 56000 , 64000 , 128000 , or 2015232 . |
Command Default
No clock rate is configured.
Command Modes
Interface configuration
Command History
Release |
Modification |
---|---|
10.0 |
This command was introduced. |
11.3 |
This command was modified to include nonstandard clock rates for the PA-8T-V35, PA-8T-X21, PA-8T-232, and PA-4T+ synchronous serial port adapters. |
12.2(33)SRA |
This command was integrated into Cisco IOS Release 12.2(33)SRA. |
12.2SX |
This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware. |
Usage Guidelines
Cable Length
Be aware that the fastest speeds might not work if your cable is too long, and that speeds faster than 148,000 bits per second are too fast for EIA/TIA-232 signaling. It is recommended that you only use the synchronous serial EIA/TIA-232 signal at speeds up to 64,000 bits per second. To permit a faster speed, use EIA/TIA-449 or V.35.
Synchronous Serial Port Adapters
For the synchronous serial port adapters (PA-8T-V35, PA-8T-X21, PA-8T-232, and PA-4T+) on Cisco 7200 series routers, and on second-generation Versatile Interface Processors (VIP2s) in Cisco 7500 series routers, the clock rate you enter is rounded (if needed) to the nearest value that your hardware can support. To display the clock rate value for the port adapter, use the showrunning-config command.
If you plan to netboot your router over a synchronous serial port adapter interface and have a boot image prior to Cisco IOS Release 11.1(9)CA that does not support nonstandard (rounded) clock rates for the port adapters, you must use one of the following standard clock rates:
-
1200
-
2400
-
4800
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9600
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19200
-
38400
-
56000
-
64000
Examples
The following example shows how to set the clock rate on the first serial interface to 64,000 bps:
Router(config)# interface serial 0
Router(config-if)# clock rate 64000
The following example shows how to set the clock rate on a synchronous serial port adapter in slot 5, port 0 to 1,234,567 bps. In this example, the clock rate is adjusted to 1,151,526 bps.
Router(config)# interface serial 5/0
Router(config-if)# clock rate 1234567
%Clockrate rounded to nearest value that your hardware can support.
The following example shows how to determine the exact clock rate that the serial interface was rounded to by using theshowrunning-config command.
Router# show running-config
Building configuration...
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!
interface Serial5/0
no ip address
clockrate 1151526
!
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