Toshiba S20LP instruction manual Appendix, Scan cycle

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Appendix

A.1 Scan cycle

In the S20LP network, each station sends out the data onto the transmission line as Packet.

The Packet is sent out onto the transmission line in the following sequence.

STN #1 STN #2 STN #3

S

Packet

Packet

Packet

S

STN #n

Packet

In the above figure,

S

means the Synchronization frame which shows the start of transmission

cycle (Scan cycle). At first, the main station sends out the Synchronization frame. Then each station sends out the Packet sequencially in the order of Station number. When the final station finishes sending out the Packet, the main station re-sends out the Synchronization frame, and the next transmission cycle is started.

The Packet consists of a Scan frame and a Message frame(s).

The Scan frame is for Scan transmission and it is sent out every time when the station becomes sender and Target Scan Timer is expired. On the other hand, the Message frame is for Message transmission and it is added only when the necessity of Message transmission is generated.

The Target Scan Time (Target Cycle Time) is a time factor for limiting the time assigned for the Message transmission. If the Scan cycle - the time from the station got Token last time to the station get Token this time - is longer than the Target Scan Time, the station sends the Scan frame but does not send the Message frame. Therefore, the Target Scan Time should be selected as longer than the time for total Scan transmission to enable the Message transmission.

The total transmission time (TSCN) can be calculated from the number of connected stations and the total size (number of words) of send data as follows.

TSCN = ( 64 + 128 * NSTN + 8 * WSCN ) / 1000 [ms]

The total message transmission time (TMSG) can be expressed as follows.

TMSG = 4 * ( 15 + 2 * WMSG ) * MSTN / 1000 [ms]

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Contents T2N/T3H stations Important Information Preface Contents Introduction to S20LP System configurationStation hardware ∙ OverviewT2N include of S20LP Port SN325 SN325∙ Status LEDs S20LP port for T2N PU245NFor SN325 ∙ Loader port ∙ Station number setting switches∙ Transmission cable connectors ∙ Reset switch only SN325Menu LS overview⎯ 10 ⎯ Specifications S20LP system specificationsS20LP-station specifications Scan transmission overview Allocation and network assignment by T-PDS Setting the data send block by S-LSSetting for data linkage Station number settingSettings on T-PDS Link PDS screen example Block Send Receive ⎯ 18 ⎯ Global ⎯ 20 ⎯ Settings on S-LS ⎯ 22 ⎯ ⎯ 23 ⎯ ⎯ 24 ⎯ ∙ Message Transmission ∙ Scan Access∙ Start with Standby mode ∙ Scan Transmission∙ Target Scan Time Data linkage example ∙ Settings on T-PDS Setting on S-LS LS setting screen 2 for STN #2 Cable connections ∙ Transmission cable breakage RAS functionBehavior in trouble ∙ Station downSelf-diagnostic function At initialization at power onDuring operation LED indication SN325T2N RAS information monitored in T2N/T3H Online map Station statusLoop map Only T2N Standby mapNumber 1-64 on the screen shows the Station number RAS information monitored on S-LSSelf Station Station No.01 Offline Select the Station Number Click the Status Display Station down information Possible error message are as followsFunction Instruction SpecificationExpanded data transfer instruction Instruction formatTransfer parameter table Parameter and construction∙ Operation Sample programRemarks PC link protocol Message transmissionMessage transmission Computer link protocol∙ Send CMD Transfer parameters aStatus B TermSTS Status Meaning Detailed Information Send completion status Transfer parameters PC link protocol transmission Data writeRID Important items Status See 7.3 5 for details on bits C, D, E, and FXW/YW PC link protocol transmission Data read ⎯ 57 ⎯ SW067 Write enabled Remarks PC link protocol transmission programLength END Scan cycle Appendix⎯ 63 ⎯ PDS remote programming PDS Setup options screen