CDDL Cerberus Dati Data Link Data Link Protocol Description Document No. Edition Supersedes e1152 07.93 CDI-135-017-E Manual Section - Copy No.
Table of contents Table of contents 1 Document History ______________________________________1 2 Scope of the Document _________________________________2 3 CDDL Protocol - physical level____________________________3 4 CDDL Protocol - Data link level ___________________________4 4.1 Transmitted data format _________________________________________ 4 4.1.1 CRC _____________________________________________________ 5 4.1.2 Control bytes masking _______________________________________ 5 4.
Document History 1 Document History Date 3.2.92 21.2.92 21.8.92 19.4.93 e1152.doc Notes Original version based on previous document STD-DOC.WPS, version 11.7.91 Document update: time-out values added English translation Title changes, document number added and DTPL 128 byte limit added Data and design subject to change without notice. Supply subject to availability © Copyright by CERBERUS AG, CH-8708 Männedorf, Switzerland 1995 07.
Scope of the Document 2 Scope of the Document This document describes the communication protocol called CDDL(Cerberus Dati Data Link). The protocol operates at physical and data link levels. It is a proprietary protocol of Cerberus Dati S.p.A. - Italy . CDDL is an asynchronous asymmetrical (in master to slave configuration) point-topoint protocol to be used in security system applications.
CDDL Protocol - physical level 3 CDDL Protocol - physical level The physical connection (ISO-OSI level "physical layer") between two devices is a RS-232-C serial line configured at 8-bit characters and 2 stop bits. The parity bit is disabled (set to none). The standard transmission rate is 9600 baud (other available transmission rates are 150, 300, 600, 1200, 2400, 4800 baud). e1152.doc Data and design subject to change without notice.
CDDL Protocol - Data link level 4 CDDL Protocol - Data link level The CDDL protocol at the data link level belongs to the "polling-selecting" type, with "stop-and-wait" transmission and positive acknowledgement. This protocol needs a master station. Usually the master is the Gateway, that starts the data transmission (polling) or asks the permission to transmit (calling) to the slave station, usually a subsystem.
CDDL Protocol - Data link level 4.1.1 CRC The CRC is composed by two bytes and it is computed using the CRC-2 polynomial including all the characters: starting from the start frame sequence, included (DLE + SOP + DTPL), to the whole packet length (DTP). The CRC-2 algorithm performs a XOR of all the characters including the starting frame sequence. The algorithm result is inserted in the message putting the most significant byte in front of the less significant byte. 4.1.
CDDL Protocol - Data link level 4.3 Calling Using the [DLE, SYN] sequence the master station requests to the slave station to be enabled to transmit a packet. If the slave station is ready to receive, it answers with the [DLE, ENQ] sequence, otherwise it sends the [DLE, EOT] (wait) sequence. The calling sequence is shown in Fig.: 3 and Fig.: 4. Fig.: 3 Fig.: 4 6 Data and design subject to change without notice.
CDDL Protocol - Data link level 4.4 Waiting The master station sends a packet without data instead of a polling sequence when it wants to signify it is no longer able to receive and manage information. The slave station answer must be [DLE, ACK] if it correctly understood the message. Otherwise the answer must be [DLE, NAK]. The waiting sequence is shown in Fig.: 5. Fig.: 5 e1152.doc Data and design subject to change without notice.
CDDL Protocol - Data link level 4.5 Errors management The transmitting station enters an answer-waiting status after sending a data packet. A successful transmission (i.e. the receiving station verifies that the CRC is correct) is signalled to the receiving station by the [DLE, ACK] sequence. The packet is transmitted again if the [DLE, NAK] sequence or any other characters is received (even if before the transmission end), as well as if the answer is missing after the T1 or T2 time.
CDDL Protocol - Data link level 4.6 Time-out control and recovery procedure These procedures are different in case of master or slave stations. Below both cases are separately described. 4.6.1 Slave side Two time counts are managed. The first time-out, T2 (see the available range in Annex A), is used to verify the continuity of the master station polling activity.
CDDL Protocol - Data link level 4.7 Control characters Here below you can find the hexadecimal control characters used by the standard protocol: DLE SOP EOP ENQ ACK SYN EOT NAK NUL 10 0DFH 007H 0EFH 005H 006H 016H 004H 015H 000H Data and design subject to change without notice. Supply subject to availability © Copyright by CERBERUS AG, CH-8708 Männedorf, Switzerland 1995 07.93 e1152.
Annex A - Protocol time-out intervals 5 Annex A - Protocol time-out intervals T1 and T2 are currently set at 1.50 seconds. This time can be changed by Cerberus Dati for specific applications. e1152.doc Data and design subject to change without notice. Supply subject to availability © Copyright by CERBERUS AG, CH-8708 Männedorf, Switzerland 1995 07.
