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How To Configure A NTP Server Using A Serial Console Session

Many NTP time servers, including TimeTools T100, T300 and T550 models, allow configuration using a serial console session. It can provide an alternative way of configuring the device if it becomes uncontactable over a network. It can also be used as a means of configuring or obtaining status information if network protocols such as HTTPS and SSH are disabled.

Establishing a serial console session requires the following items:

  • A Null-Modem cable.
  • A PC with RS232 serial COM port (or USB-serial converter).
  • PC dumb terminal emulator software such as PuTTY.

RS232 COM Port

The NTP server has a RS232 serial port at the rear of the device. The serial port has a common 9-pin D-type connector.
A PC is also required with a RS232 serial COM port. If no COM port is available, then there are plenty of after market USB to RS232 serial adapters available. These plug into a PC USB port to provide a serial COM port.

There are a number of alternative serial communications standards, such as RS422 and RS485. These cannot be used in conjunction with RS232. A RS232 COM port is required, which is by far the most common.

Once a RS232 COM port has been located, determine the COM port number assigned to the port. A COM port number is simply a port number, such as COM1 or COM2 that identifies the port. In Windows, the COM port number can generally be determined from device manager.

See Device Manager – Ports (COM &LPT).

In LINUX a serial port number can often be determined using the command ‘dmesg | grep tty’.

Null-Modem Cable

A physical link is required between the PC and the NTP server. A Null-Modem serial cable provides such a link. TimeTools supplies a Null-Modem cable with our time servers.

The Null-modem cable has a 9-Way D-type female connector at each end. The cable is wired to the following specification:

pin 2 …to… pin 3
pin 3 …to… pin 2
pin 4 …to… pin 6
pin 5 …to… pin 5
pin 6 …to… pin 4
pin 7 …to… pin 8
pin 8 …to… pin 7

Many serial leads are straight-through cables. These will not work. A Null-Modem cable that follows the above specification must be used. Ensure that the correct cable type is used.

Plug one end of the Null-Modem cable into the NTP server serial console port and the other end into the PC RS232 COM port.

PC Dumb Terminal Emulator Software

In order to communicate with the device, the PC requires software to emulate a dumb terminal –
Dumb Terminal Emulator.

The software sends keypresses at the PC keyboard to the device over the serial lead and displays characters received from the device on the screen.

There are a number of freely available PC dumb terminal emulators, the most common is PuTTY. However there are a number of others, such as TeraTerm and ZOC.

Serial Port Communications Settings

Serial line to connect to: COM port number of the PC serial port.
Speed (baud): 115200
Data Bits: 8
Stop Bits: 1
Parity: None
Flow Control: None

Andrew Shinton About Andrew Shinton
Andrew Shinton is the joint founder and Managing Director of TimeTools Limited. He has a BSc (Hons) degree in Computer Science. Andrew has over 20 years experience of GPS systems and Network Time Protocol (NTP) in the Time and Frequency Industry.