UNISCOPE MODE (FXXXX-XX)READV-RRRR-RR
3. Communications Protocol
3.6. MULTIPLEXER FUNCTION
A terminal multiplexer can determine which station in a poll group will respond to a poll.
Similarly, a UTS 30 with second screen controls the response of the displayed screen and the second screen. (The second screen is considered a separately addressable station throughout this section.) The multiplexer function, therefore, refers to a multiplexer and UTS 30 control functions.
In a poll group, the UTS 30 multiplexer function can combine an acknowledgment from one station with any traffic response from another station. This process of combining responses is called "passing" the acknowledgment. See host processor rule 3.
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The multiplexer function allows responses within the poll group to be sent in the following priority sequence:
1. A station that expected an acknowledgment but did not receive it is allowed to respond with a reply request.
2. If the priority 1 condition does not exist, a station with traffic is allowed to respond. The response may include an acknowledgment or busy response (DLE 1 or DLE ?) from that station, or a DLE 1/DLE ? passed from another station within that poll group, creating a composite message containing DLE 1 or DLE ? plus traffic.
3. If the priority 2 conditions do not exist, a station with an outstanding DLE 1 or DLE ? is allowed to respond.
4. If the priority 3 conditions do not exist, a station that has no traffic is allowed to respond to a host processor poll.
3.6.1. Rules for Handling Messages Modified by the Multiplexer Function
The following rules define the message flow for communication between the host processor and the UTS 30 as modified by the multiplexer function of a terminal multiplexer or a UTS 30 with a second screen.
• Host processor rule 3:
When using general polls, the host processor must expect an acknowledgment (DLE 1 or DLE ?) from one station to be included with a response from another station in the poll group. The multiplexer function allows an acknowledgment to be passed from one station to another station that has a traffic response pending.
• Host processor rule 4:
When using general polls, the host processor must expect successive traffic responses from stations within a poll group. However, UTS 30 rule 3 still applies. The multiplexer function allows a station with a message pending to send its response to any poll with an address it recognizes.
• Host processor rule 5:
The host processor can send text to any station in the poll group that is not owed an acknowledgment, provided the last response from the poll group is not one of the following:
DLE 1 only (SOH RID SID DID DLE 1 ETX BCC) DLE ? only (SOH RID SID DID DLE ? ETX BCC)
DLE 1 plus text available (SOH RID SID DID DLE 1 DLE 0 ETX BCC)
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• Host processor rule 6:
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When the host processor owes an acknowledgment to a station in a poll group, the host processor may send a specific poll to the poll group only if the specific poll is addressed to the station that is owed the acknowledgment.
• Host processor rule 7:
The host processor must not allow a given poll group to owe more than one acknowledgment to the host processor at any time.
3.6.2. Examples of Message Sequences Involving the Multiplexer Function
Example Sequence 1:The following message sequence applies the multiplexer function definitions and host processor rules 3, 4, 5, and 7. Rule 6 is indirectly applied in the following sequence, because the host always sends an acknowledgment before text is solicited.
In this sequence, it is assumed that the poll group defined by the multiplexer group shown in Figure 3-1 is being used.
1 . SOH 1 p p ETX BCC
2. SOH 1 a p STX data ETX BCC
3. SOH 1 p p DLE 1 ETX BCC
4. SOH 1 c p STX data ETX BCC
5. SOH 1 p p DLE 1 ETX BCC
6. EOT EOT ETX BCC
7. SOH a p STX data ETX BCC 8. SOH p p ETX BCC
9. SOH 1 e p DLE 1 STX data ETX BCC
10. SOH 1 P p DLE 1 ETX BCC
11. EQT EOT ETX BCC
Explanation:
1. General traffic poll to the poll group whose RID is "1."
2. UTS 30 text from the station whose RID is "1" and SID is "a."
3. General traffic poll with acknowledgment.
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4. UTS 30 text from the station whose RID is "1" and SID is "b." (See host processor rule 4.)
5. General traffic poll with acknowledgment.
6. No traffic.
7. Host processor text to the station whose RID is "1" and SID is "a."
8. General traffic poll.
9. Acknowledgment plus traffic where the traffic is text. The text is from the station whose RID is "1" and SID is "c." The acknowledgment was passed by the multiplexer from the station whose RID is "1" and SID is "a." (See host processor rule 3.)
10. General traffic poll with acknowledgment.
11. No traffic.
Example Sequence 2:
The following message sequence applies the multiplexer function definitions and host processor rules 3 through 7. In this sequence, it is assumed that the poll group used is the multiplexer group shown in Figure 3-1.
1. SOH 1 P p ETX BCC
2. SOH 1 a p STX data ETX BCC
3. SOH 1 P p 0 LE 1 ETX BCC
4. SOH 1 c p STX data ETX BCC
5. SOH a p STX data ETX BCC 6. SOH p p OLE 1 ETX BCC
7. SOH 1 e p 0 LE 1 STX data ETX BCC
8. SOH 1 c p STX data ETX BCC 9. SOH 1 p p OLE 1 ETX BCC
10. SOH 1 c p OLE 1 ETX BCC
11. SOH 1 p p OLE 1 ETX BCC
12. EQT EOT ETX
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14. SOH 1 P p ETX BCC
SPERRY UTS 30 SINGLE STATION System Reference
15. SOH 1 e p OLE 1 ETX BCC
16. SOH 1 P p OLE 1 ETX BCC
17. EQT EQT ETX BCC
Explanation:
1. General traffic poll to the poll group whose RID is "1."
2. UTS 30 text from the station whose RID is "1" and SID is "b."
3. General traffic poll with acknowledgment.
4. UTS 30 text from the station whose RID is "1" and SID is "b."
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5. Host processor text to the station whose RID is "1" and SID is "a." (See host processor rule 5.)
6. General traffic poll with acknowledgment.
7. Acknowledgment plus traffic where the traffic is text. The text is from the station whose RID is "1" and SID is "c." The acknowledgment was passed by the multiplexer from the station whose RID is "1" and SID is "a." (See host processor rule 3.)
8. Host processor text to the station whose RID is "1" and SID is "c." (See host processor rule 5.)
9. General traffic poll with acknowledgment.
10. Acknowledgment from the station whose RID is "1" and SID is "c."
11. General traffic poll with acknowledgment. Text cannot be sent to the poll group at this point because the last response from the poll group was acknowledgment (DLE 1 ). (See host processor rule 5.)
12. No traffic.
13. Host processor text to the station whose RID is "1" and SID is "e." (See host processor rule 5.)
14. General traffic poll.
15. Acknowledgment from the station whose RID is "1" and SID is "e."
16. General traffic poll with acknowledgment.
17. No traffic.
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