The integrated Data TAP mode in the SS20 can be instrumental in diagnosing network problems, isolating faults, setting system timing, and verifying communications integrity. The Data TAP diagnostic stream is a real-time output of the Hexadecimal data traffic passing through the SS20’s output port. This data stream can be captured by the SS20 GUI software’s Data TAP window accessed from the “Device” menu (Device > Data TAP) or by any generic ASCII terminal.
* Note: If connecting to a third part ASCII terminal set the terminal to connect to the serial port number assigned by the computer when the USB is connected (VCP port, see software installation for details) and set the serial settings to 230.4k baud : 8 data bits : No parity : 1 Stop bit, no Handshaking.
An example of the data TAP diagnostic output shown below.
P1 Tx L = 8 01 03 00 00 00 05 85 C9 P1 Rx L = 15 01 03 0A 00 00 00 00 00 00 00 00 08 B3 62 C3 P1 T = 40ms
The Data TAP output indicates the input port that the transaction came in on (P1 = COM1), the direction of the traffic (Tx/Rx) as seen at the SS20’s output port, the length of the message in bytes (L = 8 bytes), followed by the actual Hexadecimal message. Once the transaction is complete the transaction time in milliseconds (T = 40ms) is displayed. The transaction time is the time from the end of the request transmission until the receipt of the full response message. If no response was received within the timeout period *Timeout* is displayed.
* Note: The Data TAP stream indicates the data flowing through the output port of the SS20, any messages blocked by the Address Translation/Blocking functions of the SS20 will not appear in the stream. Messages with translated addresses will show the translated messages.
The transaction time shown in the data TAP stream is helpful in determining appropriate timeout values for the SS20 and upstream host/master devices. When adjusting timeout values it is recommended to monitor the Data TAP stream and watch for the maximum transaction time recorded. Set the SS20’s serial timeout to this time plus around 10% for extra headroom. It is critical to set all host/master no-response timeouts to at least double the SS20’s timeout value. This allows for a message waiting in queue time for the current transaction to complete or timeout and still have time to go out and come back with a response before the host gives up and re-tries the message.