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ACC HDLC/LAP-D Protocol User's Guide > Chapter 3 Using HDLC/LAP-D Protocol

Request Specific Processing

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Terminal Enable/Disable Requests

Enabling a non-UI terminal causes the protocol to attempt to enter multiple frame acknowledged operation (the state that allows Information frames to be exchanged). Disabling a terminal causes the non-UI terminal to exit multiple frame acknowledged operation. A newly created terminal is initially disabled. Enabling/disabling UI terminals simply allows/disallows the transmission and reception of UI frames. These requests cause unsolicited status messages to be sent by the protocol. For details regarding status codes and messages, see “Status and Error Messages”, later in this chapter.

Terminal Activate/Deactivate Requests

Activating a non-UI terminal allows the terminal to receive data (the protocol sends Receive Ready frames to indicate it is ready to receive Information frames). Deactivating the terminal prevents the terminal from receiving data (the protocol send Receive Not Ready frames). A newly created terminal is initially deactivated. For UI terminals, these requests only toggle the terminal activated flag; they do not affect the reception of data.

Write (Transmit) Requests

The data sent to the protocol via a write request becomes the information field within an I-frame or UI-frame.

The terminal must be enabled before any write requests may be sent to the terminal. In addition, for an Information frame to be sent, multiple frame acknowledged operation must have been established.

Control Requests

All control writes to this protocol share a common format. The first four bytes are defined as a header:

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Control Code

Control Length

Packet Length

Control Code

Defines the action to be taken by this request.

Control Length

The length of the data for this control request. This data immediately follows the header.

Packet Length

Some protocols allow packet data (data to be transmitted over the wire) to be passed to a control write following the control request data. For this protocol, these two bytes must be zero because the protocol does not allow packet data within a control write.

This protocol allows the following Control Codes:

5

CW_STATS

Send ST25L2STAT status message

This control write triggers the protocol to send a ST25L2STAT status message. For the format of this message, see the section on “Status and Error Messages”. Control length must be zero.

6

CW_REVCODE

Send ST25REVCD status message

This control write triggers the protocol to send a ST25REVCD status message. For the format of this message, see the section on “Status and Error Messages”. Control length must be zero.

7

CW_TIMERS

Set timers

This request is only allowed for non-UI terminals. The protocol's timers may be changed from their configured values using this control write. This request should be used with caution because the values configured with this request will not be restored if the card is reset by ZCOM.

The control request data consists of three pairs of bytes. Each pair of bytes consists of a Resolution and a Value. The legal values for Resolution are as follows: 0 = don't set, 1 = 10msec, 2 = 100msec, 3 = 1sec, 4 = 10sec.

Note that these values are different from the values used for the resolutions when configuring a terminal. The Values are used directly. A zero Value will disable the timer if the resolution is non-zero.

The first pair of bytes applies to T200, the second pair is ignored (should be set to zero) and the third pair apply to T203:

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

T200 Resolution (0-4)

T200 Value (0-255)

0

T203 Resolution (0-4)

T203 Value (0-255)

Received Data

When I-frames or UI-frames are received, the information field is sent to the associated ZLU.

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