Sepam - HV/MV Protection and control units (ENG) - Trinet

If the master requests more exchanges than necessary, the exchange numberremains unchanged and the number of usable bytes is forced to 0.To guarantee the data transfers, it is necessary to allow a response time of about500 ms between each reading operation at D300h.The first word transmitted is an exchange word. The exchange word comprisestwo fields:c the most significant byte contains the exchange number.It is incremented by 1 by the Sepam 2000 each time a successful transfer takesplace. When it reaches the value FF, it automatically goes back to zero,c the least significant byte contains the number of usable bytes in the data zone.It is initialized to zero after energizing and must be different from FFh.The exchange word may also have the following values:c xxyy: the exchange number xx must be different from FFh, the number of usablebytes in the data zone yy must be different from FFh,c 0000h: no «request frame» has been formulated yet, as it is the case, in particular,when the Sepam 2000 is switched on. The other words are not significant,c FFFFh: the «request frame» has been processed, but the results in the «replyframe» are not yet available.It is necessary to repeat «reply frame» reading. The other words are not significant.c 00FFh: the communication coupler supports the disturbance recording functionsbut not the program in the Sepam 2000 cartridge. The other words are notsignificant. However, if the master requests records from a Sepam 2000 which doesnot support the disturbance recording function at the coupler level, the Sepam 2000replies by a exception reply in the Jbus sense of the term.The words which follow the exchange word make up the data zone.Since the configuration and data files are adjacent, a Jbus frame may containthe end of the configuration file and the beginning of the data file of a record.It is up to the remote monitoring and control system software to reconstruct the filesin accordance with the transmitted number of usable bytes and the size of the filesindicated in the identification zone.Acknowledging a transferTo inform the Sepam 2000 that a record block that it has just read has been receivedcorrectly, the master must write the number of the last exchange that it has carriedout in the “exchange number” filed and set the “number of usable bytes in the datazone” of the exchange word to zero.The Sepam 2000 only increments the exchange number if the new acquisition burstsare present.Rereading the identification zoneTo ensure that the record has not been modified, during its transfer by a new record,the master rereads the contents of the identification zone and ensures thatthe recovered record date is still present.Jbus/Modbus communication35