Synchronizing a UNIX PC to a Time Server through RS-232
Spectracom Time Servers / Master Clocks have an RS-232 output port. RS-485 remote output ports are used for applications requiring long cable lengths, along with the Model 8179T TimeTap® RS-485 to RS-232 signal converter. The RS-232 ASCII data stream from these ports must be configured as either Data format 0 or Data Format 2 at 9600 baud. Refer to the appropriate Spectracom Master Clock or Time Server instruction manual for serial port or remote port configuration instructions. When using RS-232 data from a NetClock Time Server / Master Clock, the NTP4 client must be configured to use the NTP Type 4 driver. The Type 4 driver is not software. It is instructions for how to configure the NTP.conf file to accept an RS-232 interface from the Spectracom NetClock Time Server / Master Clock. The Type 4 driver configures the client software to understand the Spectracom Data Formats of 0 and 2. Refer to Dr. Mill's page on reference clock ntp drivers. For detailed information on the Type 4 driver, refer to Dr. Mill's page on the Type 4 NTP driver.
When using the Type 4 driver, the program knows to use RS-232 data from the PCs Serial port to obtain the time based on the address 127.127.4.u that is entered in the NTP.conf. file. The NTP.conf file should be located at /etc/ntp.conf (make sure all letters are lower-case). Radio and modem clocks by convention have addresses in the form 127.127.t.u, where t is the clock type and u is a unit number in the range 0-3 used to distinguish multiple instances of clocks of the same type. Since there are many different Time Formats that are supported, the driver tells the program how to obtain and process the time. The type 4 driver, for Spectracom Master Clocks or Time Servers, tells the program to use the PCs serial port to query or listen to the Time Server's or Master Clock's serial port, or a Model 8179T TimeTap, to obtain time information as needed. The driver also tells it that it is going to be either Data Format 0 or 2 at 9600 baud.
Connecting the UNIX PC to the RS-232 Port
The table below shows the minimum pin-outs for the NetClock Time Server / Master Clock serial port to be connected to the UNIX PC Com port (DB9) if building your own cable. A standard straight-thru standard serial cable may also be used if desired. Also shown are the minimum pin-outs when using a Spectracom Model 8179T TimeTap when converting from RS-485 to RS-232. You can also use the older version TimeTap, Model 8178T, but a standard straight through cable is required and a DB9 to DB25 adapter may be required.
| Time Server / Master Clock Serial Port or TimeTap |
UNIX PC Com port |
Function |
| Pin 2 |
Pin 2 |
RXD = Data input from NetClock Time Server |
| Pin 3 |
Pin 3 |
TXD = Data output to NetClock Time Server |
| Pin 5 |
Pin 5 |
Ground |
Note: when using a TimeTap and you are building your own cable without all the pins connected, jumper Pins 4 and 6 and use the external power pack connected to the TimeTap. Alternatively, use a straight-thru serial cable and disregard the jumpering of pins 4 and 6 and the use of the external power pack.