User's Manual

Chapter 3 33
Using HDLC/LAP-D Protocol
Status and Error Messages
Unsolicited Status Messages
This section describe the unsolicited status messages which may be
received on the ZLU which is set as the receiver for a terminal using this
protocol. The status codes received may or may not have bit 7 set. Bit 7 is
the down bit (masked by IO_DOWN_MASK
).Thedownbitisusedasan
indicator of the link status. When an error occurs on the link or the link
is enabled after being disabled, the protocol attempts to enter multiple
frame acknowledged operation. Until the attempt succeeds or fails, the
down bit is clear (i.e. the terminal is considered to be up until proven
otherwise). If the attempt subsequently fails, the down bit is set;
otherwise the down bit left cleared. The following status messages are
generated in response to terminal enable and disable requests
:
14 TM_TABLE_SIZE Protocol table sizes too small
The configured terminal table size is too small to allow
LAP-D to run. This status is returned in response to a
terminal creation request.
0 IO_OK No error detected
This status message is generated in response to a
terminal enable request after multiple frame
acknowledged operation is established. Note that the
down bit will always be clear.
41 IO_ALRDY_ENBL Terminal already enabled
This status message is generated in response to a
terminal enable request when the terminal is already
enabled and the protocol is not currently trying to
establish multiple frame acknowledged operation. If
the protocol is currently trying to establish multiple
frame acknowledged operation, this status message
will not be sent. Instead, either a ST25ENBL with the
down bit set or an IO_OK status message will be sent.
42 IO_ALRDY_DSBL Terminal already disabled
This status message is generated in response to a
terminal disable request when the terminal is already
disabled. The down bit will always be set.