1、STD-SMPTE RP LLL3-ENGL 197b 8357403 0002bb7 b73 SMPTE RECOMMENDED PRACTICE Supervisory Protocol for Digital Control Interface RP 11 3-1 996 Revision of RP 1 13-1 992 Page 1 of 9 pages 1 General 1.1 Scope This practice defines the supervisory protocol used within a general purpose communication chann
2、el of an interface system which transports data and digital control signals between equipment utilized in the pro- duction, post-production, and/or transmission of visual and aural information. It is intended that the supervisory protocol described in this practice be part of an overall system, allo
3、wing interconnection of pro- grammable and nonprogrammable equipment as re- quired to configure an operational system with a defined function, and to allow rapid reconfiguration of a system to provide more than one defined function utilizing a given group of equipment. 1.1.1 The primary intent of th
4、is practice is to establish supervisory procedures of the commu- nication channel for the purpose of transmitting control messages to equipment by external means. (The contents of the messages are not defined.) This practice, or sections thereof, may be applied to the interconnection of elements wit
5、hin an item of equipment. 1.2 Definitions (See figure 1 .) For the purposes of this practice, the following definitions apply: 1.2.1 bus controller: Each system contains one bus controller which supervises all tributaries in the system. Supervision is exercised through the use of this supervisory pr
6、otocol. 1.2.2 byte: A byte consists of eight bits of infor- mation. Bits used to effect transmission such as byte start, parity, or end are not part of the byte. 1.2.3 tributary: A tributary transfers messages to and from an operational device via the inter- face system. The tributary is distinct fr
7、om the function of the operational device and exists to transfer control messages between the commu- nication channel and the device. 1.2.4 word: A word consists of a byte and asso- ciated bits used to effect transmission such as start, parity, or end. 2 Message types Two types of messages shall be
8、transmitted on the channel: Supervisory messages to supervice the channel and direct the flow of device messages. Device messages to control operation of equipment functions. This type of message shall be transmitted only within standard message blocks or during device defined communications modes.
9、Details of device messages are specified in RP 138. 3 Tributary addresses Tributary addresses shall consist of two bytes: the most significant byte, which is transmitted first, and the least significant byte. The most significant bit of both bytes shall be set to binary 1. This provides an address r
10、ange starting at 8080h. Each tributary shall be assigned two unique addresses, a SELECT address and a POLL address. 3.1 Select address An address in which the least significant bit of the least significant byte equals binary O is a SELECT address. Copyright Q 1996 by the SOCIETY OF MOTION PICTURE AN
11、D TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914) 761-1 100 Approved December 10,1996 RP 113-1996 BUS CONTROLLER r- -1 HIGHER LEVELS I I-l DATA BYTE FLAG t corT t SUPERVISORY PROTOCOL 3.2 Poll address EQUIPMENT TRI BUTA RY HIGHERLEVELS -i L -_I DATA BYTE FLAG P ROTO CO L MEC
12、HANICAL I Figure 1 - System elements An address in which the least significant bit of the least significant byte equals binary 1 is a POLL address. 3.3 Group addresses Address pairs 8080-8081 h and 8082-80831, through 81FE-81FFh are reserved as GROUP SELECT ad- dresses. The addresses in which the le
13、ast significant bit of the least significant byte equals binary 1 (POLL address) shall not be used but are retained in the address numbering scheme for software considera- tions. 3.4 Discrete addresses 3.5 Address allocation table 8080-8081 h 8082-8OFFh 8180-81 FFh 8280-82FFh 64 tributaries 8380-83F
14、Fh 64 tributaries Group select - all call Group select - groups 1-63 Group select - groups 64-127 e FFSO-FFFFh 64 tributaries 4 Tributary operational states A tributary shall be in one of five major operational states: Tributary addresses shall start at 8280-8281 h. Pre- cisely 8064 discrete tributa
15、ry address pairs are avail- able. BREAK. IDLE: The tributary shall not perform any communi- cations. This state shall be exited only in response to Page 2 of 9 pages STDmSNPTE RP LL3-ENGL L77b m 8357403 0002bb9 444 m RP 113-1996 ACTIVE: Prerequisite for transition to other opera- All other superviso
16、ry characters are reserved. The tional states. The tributary shall enter this state when- use of other characters for tributary supervision is ever BREAK is received. noncompliant with this specification. POLL: The tributaryshall transmit asingle status byte to the bus controller. SELECT A single tr
17、ibutary shall enter a communica- tions mode with the bus controller. GROUP SELECT All tributaries or a selected group of tributaries shall enter a communcaton ,ode with the bus controller. 6 Operational sequences (See figure 2) 6.1 Idle Tributaries in the idle state shall not perform any communicati
18、ons sequences. 6.7.7 Idle shall be entered under the following condi- tions: - Tributary power on or reset; - Upon receipt of an (ADDR-SEL) not assigned to the tributary; - Upon receipt of a GROUP (ADDR-SEL) not assigned to the tributary; 5 Supervisory messages Tributaries shall be directed to opera
19、tional states through various communications sequences by supervisory messages as shown in figure 2. Super- visory messages consist of the following elements: BREAK: Shall drive all tributaries to the ACTIVE state. (See ANSVSMPTE 207M for code.) - When a specified time out of six words in duration o
20、ccurs; - On receipt of an undefined byte; - On encountering a transmission error or ambigu- ous condition. (ADDR-POLL): A tributary poll address (ADDR- POLL) shall drive the addressed tributary to the POLL state. (ADDR-SELECT): A tributaryse1ect address (ADDR- 6-1.2 A tributary shall exit the IDLE s
21、tate only on SEL) shall drive the addressed tributary to the SELECT state. receipt of BREAK. 6.2 Active (GROUP ADDR-SEL): A group select address shall Supervisory character: Identify communications sequences and provide status information. Supervisory characters are single bytes within the range OOh
22、-7Fh. Supervisory characters shall consist of: 01h 02 03 04 05 06 07 08 o9 Group assign Start of message Escape Acknowledge Not acknowledge Busy Reset Service request from tributary Transmit enable 6.2.1 All tributaries shall enter the ACTIVE state whenever BREAK is received and on completion of a p
23、oll sequence. 6.2.2 A tributary shall exit the ACTIVE state on receipt of an address which directs it to the POLL, SELECT, or GROUP SELECT states. A time out between the two address bytes shall cause the tributary to enter the IDLE state. 6.3 Poil The POLL state shall be used to determine the pres-
24、ence and status of a tributary. Page 3 of 9 pages RP 113-1996 STD*SMPTE RP LLI-ENGL L77b M 8357403 0002b70 Lbb W 3 O w r c i Page 4 of 9 pages STDBSMPTE RP LL3-ENGL 379b = 8357403 0002b7L UT2 6.3.1 A tributary shall enter the POLL state on receipt of its poll address (ADDR-POLL). The tributary shall
25、 transmit one supervisory character to indicate its status, then return to the ACTIVE state. Tributaries not addressed shall remain in the ACTIVE state. Supervisory characters transmitted shall be of the following: RESET (07h): Tributary has powered up or been reset since last poll; NAK (051,): An e
26、xception (time out, undefined byte, etc.) condition has occurred since last poll or select; BSY (06h): Tributary not available to receive mes- sages; If transmission from the bus controller is interrupted for more than the time-out period, the tributary shall transition to IDLE. The tributary shall
27、transfer a complete message, the byte count specified above, and a “block ready” indi- cation to the entities using the system for control. 6.4.1.2 Transmit message A tributary shall notiy the bus controller that a mes- sage is waiting by transmitting SVC (081,) during POLL. Upon receipt of TEN (0%)
28、 while in SELECT, the tributary shall transmit a standard message block as defined in 6.4.1.1. 6.4.1.3 Assign tributary to group SVC (08h): Service request from tributary; ACK (04h): Tributary available to receive messages. These characters rank in priority according to the order shown above. 6.4 Se
29、lect 6.4.1 A single tributary shall enter the SELECT state on receipt of its select address (ADDR-SEL). All other tributaries shall transition to the IDLE state. A tributary in the SELECT state shall execute the communications sequences detailed in 6.4.1.1 through 6.4.1.4 as directed by the bus cont
30、roller. 6.4.1.1 Recei.ve message Supervisory character STX (02h) shall be followed by a message block containing the following characters: - byte 1 : byte count of bytes 2 through n (O = 256 bytes). - bytes 2 through n: (256 bytes maximum) - device defined message. - byte n + 1 : checksum = twos com
31、plement of the least significant byte of the sum of bytes 1 through n. The tributary shall indicate error-free reception by responding with ACK and shall return to the SELECT state. On encountering an error during reception, the tribu- tary shall respond with NAK, then transition to IDLE. RP 113-199
32、6 Supervisory character GRP (O1 h) shall be followed by a single byte: OOh deletes all previous group assignments. If the most significant bit of the byte following GRP (01-7Fh) is a ZERO, the assignment of the tributary to the address represented by the following seven bits of that byte is deleted
33、(lh to 127h). 801, assigns the tributary to groups 1-1 27 If the most significant bit of the byte following GRP (O1 h) is a ONE, the tributary is assigned to the address represented by the following seven bits of that byte (1h to 127h). A tributary may be removed from or assigned to more than one gr
34、oup by repeating the assignment sequence. If transmission from the bus controller is interrupted for more than the time-out period between receipt of GRP and the group assignment byte, the tributary shall transition to IDLE. All group addresses except “all call” (8080h) shall be deleted at tributary
35、 power-up or reset. 6.4.1.4 Nonstandard communications Supervisory character ESC (03h) shall release a tribu- tary to nonstandard communications sequences. The tributary shall respond with ACK; it shall exit the ESC mode only in response to BREAK. Page 5 of 9 pages STD*SMPTE RP 113-ENGL L77b 8357403
36、 0002b72 T37 RP 113-1996 6.4.2 The tributary shall exit SELECT on receipt of BREAK or in response to the exceptional con- ditions noted in 6.4.1.1 through 6.4.1.3 above. 6.5 Group select 6.5.1 Groups of tributaries shall enter the GROUP SELECT state on receipt of their group select address (GROUP AD
37、DR-SEL). All tribu- taries not assigned to the group shall transition to IDLE. Tributaries in the GROUP SELECT state shall execute the communications se- quences detailed in 6.5.1.1 and 6.5.1.2 as di- rected by the bus controller. 6.5.1.1 Receive message Supervisory character STX shall be followed b
38、y a message block as defined in 6.4.1.1. Each tributary returns to GROUP SELECT state after error-free reception of the block; no response shall be transmitted. On encountering an error during reception, a tributary shall respond with NAK, then transition to IDLE. If transmission from the bus contro
39、ller is interrupted for more than the time-out period, tributaries shall transition to IDLE. 6.5.1.2 Nonstandard communications Supervisory character ESC shall release a group to nonstandard communications in accordance with 6.4.1.4. Tributaries shall exit this mode only in re- sponse to BREAK. 6.5.
40、2 Tributaries shall exit GROUP SELECT on receipt of BREAK or in response to the excep- tional conditions noted in 6.5.1.1. 7 Bus controller operation 7.1 System synchronization The bus controller shall transmit BREAK when power is turned on and after being reset. 7.2 Tributary response time out The
41、bus controller shall transmit BREAK when a tributary fails to respond within the following time-out periods: - In response to ADDR-POLL, GRP (#), ESC, TEN, END OF MSG BLOCK - 6 words. 8 Guidelines 8.1 Function of this practice This practice specifies the supervisory protocol used within the communic
42、ation channel. The protocol is the sequence of characters used to transfer mes- sages between the bus controller and tributaries, provide recovery from error conditions, and generally supervise the usage of the communication channel. This practice is concerned only with channel supervi- sion. Electr
43、ical/mechanicaI characteristics are speci- fied in separate standards since many types of channels which can deliver eight-bit binary bytes and a unique BREAK condition can operate under super- vision of the protocol. Message content is specified by standards which are independent of both electri- c
44、al/mechanical and supervisory Characteristics of the communication channel. 8.2 System configurations This supervisory protocol permits supervision of point- to-point and multipoint systems. A point-to-point con- figuration is one in which acommunication channel is connected to only one tributary. T
45、he bus controller may be connected to more than one channel, each having one tributary. This configuration has the ad- vantage of speed since the dedicated channels pro- vide access to all tributaries simultaneously. The multipoint bus configuration is one in which more than one tributary is connect
46、ed to a channel. This configuration has the advantage of reduced cabling costs and complexity. The main disadvantage of mul- tipoint is that messages to different tributaries must queue up and be sent serially on the bus. This configuration is therefore slower in response time than point-to-point sy
47、stems. 8.3 State diagrams The supervisory procedures are described by means of state diagrams that show how the interfacing hard- Page 6 of 9 pages STD-SMPTE RP 113-ENGL 177b = 8357401 0002b73 975 RP 11 3-1 996 ware and software in a tributary follow sequences of bytes as they are received from the
48、communication channel. 8.3.1 Each state (condition) that a tributary can assume is represented graphically as a circle; major states are identified by an upper case label or mnemonic within the circle: RESET O 8.3.2 All possible transitions between states are represented by arrows between the states
49、; each transition is qualified by an expression which will produce the transition: STATE 3 8.3.3 Expressions can be messages received from or transmitted to the communication chan- nel, or local messages generated within the tributary. 8.3.3.1 Messages received from the channel are represented by R followed by the received mes- sage in parentheses: indicates transition from state ONE to state TWO on receipt of the message GRP. 8.3.3.2 Messages transmitted to the bus are rep- resented by T followed by the transmitted mes- sage in parentheses: indicates transition fr
