HOST PROCESSOR PROGRAMMING SUGGESTIONS

3.11.1. Handling the Acknowledgment/Busy-Plus-Traffic Response

U P-9799 Rev. 1

In a poll group, the UTS 30 multiplexer function can combine an acknowledgment from one station with any traffic response from another station.

When an acknowledgment/busy-plus-traffic response is returned by a station that just received host processor text, the acknowledgment/busy portion of the response is from that station and was not passed from another station by the multiplexer function. Possible acknowledgment/

busy-plus-traffic poll responses from a station that just received host processor text are as follows:

• OLE 1 plus message-waiting or program-attention key code (3.9.2)

• OLE 1 plus peripheral selection delayed (UTS 30 rule 8)

• OLE 1 plus message-queued (UTS 30 rule 8)

• OLE 1 plus peripheral status (UTS 30 rule 8)

• OLE 1 plus text (poll response following host processor text containing a transmit function)

• OLE 1 plus THRU (UTS 30 rule 7)

• OLE ? plus message-waiting or program-attention key code (3.9.2)

Passing the acknowledgment/busy response by the multiplexer function does not take place, and all considerations concerning the passing of this response are eliminated, under the following conditions:

• When the host processor text to a station is followed by a specific poll to that station

• When each poll group has only one station and, therefore, a general poll is recognized only by that station

However, the use of general polls and the configuration of poll groups with more than one station produce the most efficient communications exchange (that is, the minimum number of messages).

The host processor may be programmed to handle acknowledgment/busy-plus-traffic responses resulting from general polls by retaining, at the line level, the address of the station from which the host processor expects an acknowledgment. If the station address contained in the response is that of the station from which an acknowledgment is expected, then both the acknowledgment/busy and the traffic portion of the response will be processed for that station.

If, however, the station address contained in the response is different from the address of the station from which an acknowledgment is expected, then the acknowledgment/busy portion of the response will be processed for the station from which an acknowledgment is expected, and

UP-9799 Rev. 1

SPERRY UTS 30 SINGLE STATION System Reference

3.11.2. Passing the Acknowledgment/Busy Response in TEXT/SD, TEXT/Pl, or TEXT /SD/Pl Messages

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Whenever TEXT/SD, TEXT/Pl, or TEXT/SD/Pl messages are being sent by the host processor, the acknowledgment in the response must not be interpreted as meaning a successful peripheral selection or successful completion of the peripheral operation. In the acknowledgment/plus-traffic combination shown in Table A-1 (peripheral status responses), it is possible for the acknowledgment portion of the response to be passed by the multiplexer function to another station; if the acknowledgment portion is passed to another station, the response to a general poll following the host processor text message will contain only the acknowledgment portion of the original acknowledgment-plus-traffic response. Therefore, the host processor must wait for a subsequent poll response containing the traffic portion of the original acknowledgment-plus-traffic response to determine the status of the peripheral selection and/or operation.

The following message sequence illustrates how the acknowledgment should be interpreted. In this sequence, the station whose RID is "1" and SID is "b" contains the UTS 30 second screen, whose SID is "c."

1. SQH 1 c t STX data OC2 ETX BCC 2. SQH 1 P p ETX BCC

3. SQH 1 e p OLE 1 STX data ETX BCC

4. SQH 1 P p OLE 1 ETX BCC

5. SQH 1 c t OLE 4 ETX BCC

6. SQH 1 P p 0 LE 1 ETX BCC

7. EQT EQT ETX BCC

Explanation:

1. TEXT/SD/Pl message directed to the printer through the station whose RID is "1" and SID is "b."

2. General traffic poll to the poll group whose RID is "1."

3. Acknowledgment-plus-traffic message where the traffic is text from the station whose RID is "1" and SID is "c." The acknowledgment was passed from the station that was sent the TEXT/SD/Pl message in step 1 (station 1 c)~

4. General traffic poll with acknowledgment.

5. Message-queued (DLE 4) response. Originally, the station response was to contain acknowledgment plus message queued (DLE 1 DLE 4); however, the acknowledgment from the station was passed by the multiplexer function and had already been sent in step 3.

6. General traffic poll with acknowledgment.

7. No traffic.

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3.11.3. Line Error Recovery

SPERRY UTS 30 SINGLE STATION

System Reference UP-9799 Rev. 1

The UTS 30 is designed to allow recovery from communications line errors without loss or duplication of messages. The line error recovery rules discussed in 3.7 must be followed.

The host processor should follow these guidelines to facilitate line error recovery:

• The error recovery sequence should be completed when the line error occurs.

• The address of the station which was just sent host processor text and therefore owes the host processor an acknowledgment, should be retained.

• Not more than one station at a time should be put on the line in a state where it has an acknowledgment to send.

• The previous poll response type (such as UTS 30 text, acknowledgment, or acknowledgment-plus-THAU) should be retained.

• The address of the previous poll response should be retained.

UP-9799 Rev. 1

4.1. GENERAL

SPERRY UTS 30 SINGLE STATION

System Reference 4-1

4. UTS 30 and Host Processor